1,2,4-Oxadiazole and Thiadiazole Compounds as Immunomodulators

ABSTRACT

The present invention relates to 1,2,4-oxadiazole and thiadiazole compounds of formula (I) and their use to inhibit the programmed cell death 1 (PD1) signaling pathway and/or for treatment of disorders by inhibiting an immunosuppressive signal induced by PD-1, PD-L1 or PD-L2.

This application is a continuation under 35 U.S.C. § 120 of pendingapplication U.S. Ser. No. 16/945,854, filed Aug. 1, 2020, which is acontinuation of U.S. Ser. No. 15/556,800, filed Sep. 8, 2017, now U.S.Pat. No. 10,590,093, which is a national stage application under 35U.S.C. § 371 of PCT/IB2016/051266, filed Mar. 7, 2016, now abandoned,which claims the benefit of Indian provisional application number1180/CHE/2015, filed on Mar. 10, 2015, now abandoned, and Indianprovisional application number 1178/CHE/2015, filed on Mar. 10, 2015,now abandoned; the specifications of all of which are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates to 1,2,4-oxadiazole and thiadiazolecompounds and their derivatives therapeutically useful as immunemodulators. The invention also relates to pharmaceutical compositionscomprising 1,2,4-oxadiazole and thiadiazole compounds and theirderivatives.

BACKGROUND OF THE INVENTION

Programmed cell death-1 (PD-1) is a member of the CD28 superfamily thatdelivers negative signals upon interaction with its two ligands, PD-L1or PD-L2. PD-1 and its ligands are broadly expressed and exert a widerrange of immunoregulatory roles in T cells activation and tolerancecompared with other CD28 members. PD-1 and its ligands are involved inattenuating infectious immunity and tumor immunity and facilitatingchronic infection and tumor progression. The biological significance ofPD-1 and its ligand suggests the therapeutic potential of manipulationof PD-1 pathway against various human diseases (Hyun-Tak Jin, et al.,Curr Top Microbiol Immunol. (2011); 350:17-37).

T-cell activation and dysfunction relies on direct and modulatedreceptors. Based on their functional outcome, co-signaling molecules canbe divided as co-stimulators and co-inhibitors, which positively andnegatively control the priming, growth, differentiation and functionalmaturation of a T-cell response (Li Shi, et al., Journal of Hematology &Oncology 2013, 6:74).

Therapeutic antibodies that block the programmed cell death protein-1(PD-1) immune checkpoint pathway prevent T-cell down regulation andpromote immune responses against cancer. Several PD-1 pathway inhibitorshave shown robust activity in various phases of clinical trials (R DHarvey, Clinical Pharmacology & Therapeutics (2014); 96 2, 214-223).

Programmed death-1 (PD-1) is a co-receptor that is expressedpredominantly by T cells. The binding of PD-1 to its ligands, PD-L1 orPD-L2, is vital for the physiological regulation of the immune system. Amajor functional role of the PD-1 signaling pathway is the inhibition ofself-reactive T cells, which serve to protect against autoimmunediseases. Elimination of the PD-1 pathway can therefore result in thebreakdown of immune tolerance that can ultimately lead to thedevelopment of pathogenic autoimmunity. Conversely, tumor cells can attimes co-opt the PD-1 pathway to escape from immunosurveillancemechanisms. Therefore, blockade of the PD-1 pathway has become anattractive target in cancer therapy. Current approaches include sixagents that are either PD-1 and PD-L1 targeted neutralizing antibodiesor fusion proteins. More than forty clinical trials are underway tobetter define the role of PD-1 blockade in variety of tumor types (ArielPedoeem et al., Clinical Immunology (2014), 153(1), 145-152).

International applications WO2002086083, WO2004004771, WO2004056875,WO2006121168, WO2008156712, WO2010077634, WO2011066389, WO2014055897 andWO2014100079 report PD-1, PD-L1 inhibitory antibodies and/or methods ofidentifying such antibodies. Further, US patents such as U.S. Pat. Nos.8,735,553 and 8,168,757 report PD-1 or PD-L1 inhibitory antibodiesand/or fusion proteins.

Furthermore, International applications, WO2011161699, WO2012168944,WO2013144704 and WO2013132317 report peptides or peptidomimeticcompounds which are capable of suppressing and/or inhibiting theprogrammed cell death 1 (PD1) signaling pathway.

Still there is a need for more potent, better and/or selective immunemodulators of the PD-1 pathway.

SUMMARY OF INVENTION

The present invention provides 1,2,4-oxadiazole and thiadiazolecompounds and their pharmaceutically acceptable salts or stereoisomers.These compounds are capable of suppressing and/or inhibiting theprogrammed cell death 1 (PD1) signalling pathway.

In one aspect, the present invention provides 1,2,4-oxadiazole andthiadiazole compounds of formula (I):

or a pharmaceutically acceptable salt or a stereoisomer thereof;wherein,

----- is an optional double bond;

X is O or S;

R₁ and R₂ independently are a side chain of an amino acid or hydrogen,(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl or cycloalkyl; wherein(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl and cycloalkyl areoptionally substituted by one or more substituents selected from amino,alkylamino, acylamino, carboxylic acid, carboxylate, carboxylic acidester, thiocarboxylate, thioacid, —CONR₇R₈, hydroxy, cycloalkyl,(cycloalkyl)alkyl, aryl, arylalkyl, heterocyclyl, (heterocyclyl)alkyl,heteroaryl, (heteroaryl)alkyl, guanidino, —SH and —S(alkyl); optionallywherein cycloalkyl, aryl, heterocyclyl and heteroaryl are furthersubstituted by one or more substituents such as hydroxy, alkoxy, halo,amino, nitro, cyano or alkyl and optionally wherein two or three carbonatoms of the (C₁-C₆)alkyl, (C₂-C₆)alkenyl or (C₂-C₆)alkynyl form part ofa 3-7-membered carbocyclic or heterocyclic ring (such as a cyclobutyl oroxirane ring);

R₃ is hydrogen, —CO-[Aaa1]_(m), [Aaa1]_(m), [Aaa1]_(m)—CO-[Aaa1]_(m),—S(O)_(p)-[Aaa1]_(m), —CONR₇R₈, —COR_(c), —SO₂R_(c), (C₁-C₆)alkyl,(C₂-C₆)alkenyl or (C₂-C₆)alkynyl; wherein (C₁-C₆)alkyl, (C₂-C₆)alkenyland (C₂-C₆)alkynyl are optionally substituted by one or moresubstituents selected from amino, alkylamino, acylamino, —COO-alkyl,carboxylic acid, carboxylate, thiocarboxylate, thioacid, —CONR₇R₈,hydroxy, aryl, arylalkyl, cycloalkyl, heterocyclyl, heteroaryl,(cycloalkyl)alkyl, (heterocyclyl)alkyl, (heteroaryl)alkyl, guanidino,—SH and —S(alkyl); optionally wherein cycloalkyl, aryl, heterocyclyl andheteroaryl are further substituted by one or more substituents such ashydroxy, alkoxy, halo, amino, nitro, cyano or alkyl, optionally whereintwo or three carbon atoms of the (C₁-C₆)alkyl, (C₂-C₆)alkenyl or(C₂-C₆)alkynyl form part of a 3-7-membered carbocyclic or heterocyclicring (such as a cyclobutyl or oxirane ring);

R₄ and R₅ independently are hydrogen or absent;

R₆ is hydrogen, alkyl, alkenyl, alkynyl, aralkyl, aryl, heteroaralkyl,heteroaryl, cycloalkyl, (cycloalkyl)alkyl, amino, aminoalkyl,hydroxyalkyl, alkoxyalkyl, acyl, [Aaa2]_(n), —CO-[Aaa2]_(n),[Aaa2]_(n)—CO-[Aaa2]_(n) or —S(O)_(p)-[Aaa2]_(n);

R₇ and R₈ independently are hydrogen, (C₁-C₆)alkyl, (C₂-C₆)alkenyl,(C₂-C₆)alkynyl, aryl or heterocyclyl; wherein (C₁-C₆)alkyl,(C₂-C₆)alkenyl and (C₂-C₆)alkynyl, aryl and heterocyclyl are optionallysubstituted by one or more substituents selected from halogen, hydroxyl,amino, nitro, cyano, cycloalkyl, heterocyclyl, heteroaryl, aryl,guanidino, (cycloalkyl)alkyl, (heterocyclyl)alkyl and (heteroaryl)alkyl;optionally wherein two or three carbon atoms of the (C₁-C₆)alkyl,(C₂-C₆)alkenyl or (C₂-C₆)alkynyl form part of a 3-7-membered carbocyclicor heterocyclic ring (such as a cyclobutyl or oxirane ring);

alternatively R₇ and R₈ together with the nitrogen to which they areattached form an optionally substituted 3-7-membered ring containing 0-2additional heteroatoms independently selected from N, O and S in anystable combination; wherein the optional substituent at each occurrenceis selected from hydroxyl, —COOH, —COO-alkyl, amide, halo, amino, nitroand cyano;

[Aaa1] and [Aaa2], independently for each occurrence, represents anamino acid residue; wherein a C-terminal carboxyl group of amino acidresidue is a free C-terminal carboxyl group (—COOH) or a modifiedC-terminal carboxyl group and an N-terminal amino group of amino acidresidue is a free N-terminus (—NH₂) or a modified N-terminal aminogroup;

R_(a) is hydrogen or alkyl, alkenyl, alkynyl, acyl, aralkyl, aryl,heteroaralkyl, heteroaryl, cycloalkyl, (cycloalkyl)alkyl, aminoalkyl,hydroxyalkyl or alkoxyalkyl; R_(b) is hydrogen or alkyl, alkenyl,alkynyl, acyl, aralkyl, aryl, heteroaralkyl, heteroaryl, cycloalkyl,(cycloalkyl)alkyl, aminoalkyl, hydroxyalkyl or alkoxyalkyl; or R_(b) andR₂, together with the atoms to which they are attached, may formpyrrolidine or piperidine optionally substituted with one or more groupsindependently selected from hydroxyl, halo, amino, cyano and alkyl;

R_(c) is (C₁-C₆)alkyl, cycloalkyl, aryl, heterocyclcyl or heteroaryl;wherein the said (C₁-C₆)alkyl, cycloalkyl, aryl, heterocyclcyl orheteroaryl is optionally substituted by one or more substituentsselected from carboxylic acid, hydroxyl, alkyl, alkoxy, amino,alkylamino, acylamino, carboxylic ester, cycloalkyl, heterocyclyl,heteroaryl, (cycloalkyl)alkyl, (heterocyclyl)alkyl or (heteroaryl)alkyl;

m and n independently are integers selected from 1 to 3;

p is an integer selected from 1 to 2;

with a proviso that R₁ is not a side chain of Ser or Thr, when R₂ is aside chain of Asp, Asn, Glu or Gln, R₃ is hydrogen, —CO-Ser or —CO-Thr,R is hydrogen, alkyl or acyl and R_(a) and R_(b) are hydrogen.

In another aspect, the present invention relates to a process forpreparation of compounds of formula (I) or a pharmaceutically acceptablesalt or a stereoisomer thereof.

In a further aspect, the present invention relates to pharmaceuticalcompositions comprising a compound of formula (I) or a pharmaceuticallyacceptable salt or a stereoisomer thereof and processes for preparingsuch compositions.

Yet another aspect of the present invention provides methods ofadministering a compound of formula (I) or a pharmaceutically acceptablesalt or a stereoisomer, to suppress and/or inhibit the programmed celldeath 1 (PD1) signaling pathway. For example, these compounds can beused to treat one or more diseases characterized by aberrant orundesired activity of the PD1 signaling pathway.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides 1,2,4-oxadiazole and thiadiazolecompounds and their derivatives as therapeutic agents useful fortreatment of disorders via immunopotentiation comprising inhibition ofimmunosuppressive signal induced due to PD-1, PD-L1 or PD-L2 andtherapies using them.

Each embodiment is provided by way of explanation of the invention andnot by way of limitation of the invention. In fact, it will be apparentto those skilled in the art that various modifications and variationscan be made to the compounds, compositions and methods described hereinwithout departing from the scope or spirit of the invention. Forinstance, features illustrated or described as part of one embodimentcan be applied to another embodiment to yield a still furtherembodiment. Thus it is intended that the present invention include suchmodifications and variations and their equivalents. Other objects,features and aspects of the present invention are disclosed in or areobvious from, the following detailed description. It is to be understoodby one of ordinary skill in the art that the present discussion is adescription of exemplary embodiments only and is not to be construed aslimiting the broader aspects of the present invention.

In certain embodiments, the present invention provides compounds offormula (I):

or a pharmaceutically acceptable salt or a stereoisomer thereof;wherein,

----- is an optional double bond;

X is O or S;

R₁ and R₂ independently are a side chain of an amino acid or hydrogen,(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl or cycloalkyl; wherein(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl and cycloalkyl areoptionally substituted by one or more substituents selected from amino,alkylamino, acylamino, carboxylic acid, carboxylate, carboxylic acidester, thiocarboxylate, thioacid, —CONR₇R₈, hydroxy, cycloalkyl,(cycloalkyl)alkyl, aryl, arylalkyl, heterocyclyl, (heterocyclyl)alkyl,heteroaryl, (heteroaryl)alkyl, guanidino, —SH and —S(alkyl); optionallywherein cycloalkyl, aryl, heterocyclyl and heteroaryl are furthersubstituted by one or more substituents such as hydroxy, alkoxy, halo,amino, nitro, cyano or alkyl and optionally wherein two or three carbonatoms of the (C₁-C₆)alkyl, (C₂-C₆)alkenyl or (C₂-C₆)alkynyl form part ofa 3-7-membered carbocyclic or heterocyclic ring (such as a cyclobutyl oroxirane ring);

R₃ is hydrogen, —CO-[Aaa1]_(m), [Aaa1]_(m), [Aaa1]_(m)—CO-[Aaa1]_(m),—S(O)_(p)-[Aaa1]_(m), —CONR₇R₈, —COR_(c), —SO₂R_(c), (C₁-C₆)alkyl,(C₂-C₆)alkenyl or (C₂-C₆)alkynyl; wherein (C₁-C₆)alkyl, (C₂-C₆)alkenyland (C₂-C₆)alkynyl are optionally substituted by one or moresubstituents selected from amino, alkylamino, acylamino, —COO-alkyl,carboxylic acid, carboxylate, thiocarboxylate, thioacid, —CONR₇R₈,hydroxy, aryl, arylalkyl, cycloalkyl, heterocyclyl, heteroaryl,(cycloalkyl)alkyl, (heterocyclyl)alkyl, (heteroaryl)alkyl, guanidino,—SH and —S(alkyl); optionally wherein cycloalkyl, aryl, heterocyclyl andheteroaryl are further substituted by one or more substituents such ashydroxy, alkoxy, halo, amino, nitro, cyano or alkyl, optionally whereintwo or three carbon atoms of the (C₁-C₆)alkyl, (C₂-C₆)alkenyl or(C₂-C₆)alkynyl form part of a 3-7-membered carbocyclic or heterocyclicring (such as a cyclobutyl or oxirane ring);

R₄ and R₅ independently are hydrogen or absent;

R₆ is hydrogen, alkyl, alkenyl, alkynyl, aralkyl, aryl, heteroaralkyl,heteroaryl, cycloalkyl, (cycloalkyl)alkyl, amino, aminoalkyl,hydroxyalkyl, alkoxyalkyl, acyl, [Aaa2]_(n), —CO-[Aaa2]_(n),[Aaa2]_(n)—CO-[Aaa2]_(n) or —S(O)_(p)-[Aaa2]_(n);

R₇ and R₈ independently are hydrogen, (C₁-C₆)alkyl, (C₂-C₆)alkenyl,(C₂-C₆)alkynyl, aryl or heterocyclyl; wherein (C₁-C₆)alkyl,(C₂-C₆)alkenyl and (C₂-C₆)alkynyl, aryl and heterocyclyl are optionallysubstituted by one or more substituents selected from halogen, hydroxyl,amino, nitro, cyano, cycloalkyl, heterocyclyl, heteroaryl, aryl,guanidino, (cycloalkyl)alkyl, (heterocyclyl)alkyl and (heteroaryl)alkyl;optionally wherein two or three carbon atoms of the (C₁-C₆)alkyl,(C₂-C₆)alkenyl or (C₂-C₆)alkynyl form part of a 3-7-membered carbocyclicor heterocyclic ring (such as a cyclobutyl or oxirane ring);

alternatively R₇ and R₈ together with the nitrogen to which they areattached form an optionally substituted 3-7-membered ring containing 0-2additional heteroatoms independently selected from N, O and S in anystable combination; wherein the optional substituent at each occurrenceis selected from hydroxyl, —COOH, —COO-alkyl, amide, halo, amino, nitroand cyano;

[Aaa1] and [Aaa2], independently for each occurrence, represents anamino acid residue; wherein a C-terminal carboxyl group of amino acidresidue is a free C-terminal carboxyl group (—COOH) or a modifiedC-terminal carboxyl group and an N-terminal amino group of amino acidresidue is a free N-terminus (—NH₂) or a modified N-terminal aminogroup;

R_(a) is hydrogen or alkyl, alkenyl, alkynyl, acyl, aralkyl, aryl,heteroaralkyl, heteroaryl, cycloalkyl, (cycloalkyl)alkyl, aminoalkyl,hydroxyalkyl or alkoxyalkyl; R_(b) is hydrogen or alkyl, alkenyl,alkynyl, acyl, aralkyl, aryl, heteroaralkyl, heteroaryl, cycloalkyl,(cycloalkyl)alkyl, aminoalkyl, hydroxyalkyl or alkoxyalkyl; or R_(b) andR₂, together with the atoms to which they are attached, may formpyrrolidine or piperidine optionally substituted with one or more groupsindependently selected from hydroxyl, halo, amino, cyano and alkyl;

R_(c) is (C₁-C₆)alkyl, cycloalkyl, aryl, heterocyclcyl or heteroaryl;wherein the said (C₁-C₆)alkyl, cycloalkyl, aryl, heterocyclcyl orheteroaryl is optionally substituted by one or more substituentsselected from carboxylic acid, hydroxyl, alkyl, alkoxy, amino,alkylamino, acylamino, carboxylic ester, cycloalkyl, heterocyclyl,heteroaryl, (cycloalkyl)alkyl, (heterocyclyl)alkyl or (heteroaryl)alkyl;

m and n independently are integers selected from 1 to 3;

p is an integer selected from 1 to 2;

with a proviso that R₁ is not a side chain of Ser or Thr, when R₂ is aside chain of Asp, Asn, Glu or Gln, R₃ is hydrogen, —CO-Ser or —CO-Thr,R_(e) is hydrogen, alkyl or acyl and R_(a) and R_(b) are hydrogen.

In certain embodiments of the compound of formula (I): or apharmaceutically acceptable salt or a stereoisomer thereof; wherein,

----- is an optional double bond;

X is O or S;

R₁ and R₂ independently are a side chain of an amino acid or hydrogen,(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl or cycloalkyl; wherein(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl and cycloalkyl areoptionally substituted by one or more substituents selected from amino,alkylamino, acylamino, carboxylic acid, carboxylate, thiocarboxylate,thioacid, —CONR₇R₈, hydroxy, cycloalkyl, (cycloalkyl)alkyl, aryl,heterocyclyl, heteroaryl, guanidino, —SH and —S(alkyl); optionallywherein cycloalkyl, aryl, heterocyclyl and heteroaryl are furthersubstituted by one or more substituents such as hydroxy, alkoxy, halo,amino, nitro, cyano or alkyl;

R₃ is hydrogen, —CO-[Aaa1]_(m), [Aaa1]_(m), [Aaa1]_(m)—CO-[Aaa1]_(m),—S(O)_(p)-[Aaa1]_(m), —CONR₇R₈, —COR_(c), —SO₂R_(c), (C₁-C₆)alkyl,(C₂-C₆)alkenyl or (C₂-C₆)alkynyl; wherein (C₁-C₆)alkyl, (C₂-C₆)alkenyland (C₂-C₆)alkynyl are optionally substituted by one or moresubstituents selected from amino, alkylamino, acylamino, carboxylicacid, carboxylate, thiocarboxylate, thioacid, —CONR₇R₈, hydroxy,cycloalkyl, aryl, heterocyclyl, heteroaryl, guanidino, —SH and—S(alkyl); optionally wherein cycloalkyl, aryl, heterocyclyl andheteroaryl are further substituted by one or more substituents such ashydroxy, alkoxy, halo, amino, nitro, cyano or alkyl;

R₄ and R₅ independently are hydrogen or absent;

R₆ is hydrogen, alkyl, acyl, [Aaa2]_(n). —CO-[Aaa2]_(n),[Aaa2]_(n)—CO-[Aaa2]_(n) or —S(O)_(p)-[Aaa1]_(n);

R₇ and R₈ independently are hydrogen, (C₁-C₈)alkyl, (C₂-C₆)alkenyl,(C₂-C₆)alkynyl, aryl or heterocyclyl; wherein (C₁-C₆)alkyl,(C₂-C₆)alkenyl and (C₂-C₆)alkynyl, aryl and heterocyclyl are optionallysubstituted by one or more substituents selected from halogen, hydroxyl,amino, nitro, cyano, cycloalkyl, heterocyclyl, heteroaryl, aryl,guanidino, (cycoalkyl)alkyl, (heterocyclyl)alkyl and (heteroaryl)alkyl;optionally wherein two or three carbon atoms of the (C₁-C₆)alkyl,(C₂-C₆)alkenyl or (C₂-C₆)alkynyl form part of a 3-7-membered carbocyclicor heterocyclic ring (such as a cyclobutyl or oxirane ring);

alternatively R₇ and R₈ together with the nitrogen to which they areattached form an optionally substituted 3-7-membered ring containing 0-2additional heteroatoms independently selected from N, O and S in anystable combination; wherein the optional substituent at each occurrenceis selected from hydroxyl, —COOH, —COO-alkyl, amide, halo, amino, nitroand cyano;

each of [Aaa1] and [Aaa2] is independently selected amino acid residues;wherein C-terminal carboxyl group of amino acid residue is a freeC-terminal carboxyl group (—COOH) or a modified C-terminal carboxylgroup and N-terminal amino group of amino acid residue is a freeN-terminus (—NH₂) or a modified N-terminal amino group;

R_(a) is hydrogen or alkyl;

R_(b) is hydrogen or alkyl; or R_(b) and R₂, together with the atoms towhich they are attached, may form pyrrolidine or piperidine optionallysubstituted with one or more groups independently selected fromhydroxyl, halo, amino, cyano and alkyl;

R_(c) is (C₁-C₆)alkyl, cycloalkyl, aryl, heterocyclcyl or heteroaryl;wherein the said (C₁-C₆)alkyl, cycloalkyl, aryl, heterocyclcyl orheteroaryl is optionally substituted by one or more substituentsselected from carboxylic acid, hydroxyl, alkyl, alkoxy, amino,alkylamino, acylamino, carboxylic ester, cycloalkyl, heterocyclyl,heteroaryl, (cycloalkyl)alkyl, (heterocyclyl)alkyl or (heteroaryl)alkyl;

m and n independently are integers selected from 1 to 3;

p is an integer selected from 1 to 2;

with a proviso that R₁ is not a side chain of Ser or Thr, when R₂ is aside chain of Asp, Asn, Glu or Gln, R₃ is hydrogen, —CO-Ser or —CO-Thr,R₆ is hydrogen, alkyl or acyl and R_(a) and R_(b) are hydrogen.

In certain embodiments the compounds of the invention are represented byformula (I),

wherein,

X is O or S;

each dotted line [----] independently represents an optional doublebond;

R_(a) and R_(b) are each independently hydrogen or a substituent, suchas alkyl, alkenyl, alkynyl, acyl, aralkyl, aryl, heteroaralkyl,heteroaryl, cycloalkyl, (cycoalkyl)alkyl, aminoalkyl, hydroxyalkyl oralkoxyalkyl;

R₁ is (C₁-C₆)alkyl substituted by one or more substituents selected fromamino, alkylamino, acylamino, heterocyclyl, heteroaryl, guanidino,(heterocyclyl)alkyl and (heteroaryl)alkyl, wherein any heterocyclyl orheteroaryl contains at least one nitrogen atom and R₁ includes a basicnitrogen atom whose conjugate acid has a pKa above 3, preferably above 5and optionally wherein two or three carbon atoms of the (C₁-C₆)alkyl,(C₂-C₆)alkenyl or (C₂-C₆)alkynyl form part of a 3-7-membered carbocyclicor heterocyclic ring (such as a cyclobutyl or oxirane ring);

R₂ is (C₁-C₆)alkyl, (C₂-C₆)alkenyl or (C₂-C₆)alkynyl substituted by oneor more substituents selected from carboxylate, carboxylic acid,carboxylic acid ester, thiocarboxylate, thio acid, amido, amino andheterocyclyl, optionally wherein two or three carbon atoms of the(C₁-C₆)alkyl, (C₂-C₆)alkenyl or (C₂-C₆)alkynyl form part of a3-7-membered carbocyclic or heterocyclic ring (such as a cyclobutyl oroxirane ring);

R₃ is hydrogen or —CO-Aaa;

Aaa represents an amino acid residue, wherein the amino acid residuecomprises a side chain that includes a —OH, —O-acyl, —SH, —NH₂ orNH(alkyl) moiety;

each of R₄ and R₅ independently is hydrogen or absent; and

R₆ represents hydrogen, alkyl, alkenyl, alkynyl, aralkyl, aryl,heteroaralkyl, heteroaryl, cycloalkyl, (cycloalkyl)alkyl, amino,aminoalkyl, hydroxyalkyl, alkoxyalkyl or acyl;

or a pharmaceutically acceptable salt thereof.

In yet further embodiments of the compound of formula (I):

or a pharmaceutically acceptable salt or a stereoisomer thereof;wherein,

----- is an optional double bond;

X is O or S;

R₁ and R₂ independently are a side chain of an amino acid or(C₁-C₆)alkyl, (C₂-C₆)alkenyl or (C₂-C₆)alkynyl; wherein (C₁-C₆)alkyl,(C₂-C₆)alkenyl and (C₂-C₆)alkynyl are substituted by one or moresubstituents selected from amino, alkylamino, acylamino, —COO— alkyl,cycloalkyl, heterocyclyl, heteroaryl, guanidino, (cycloalkyl)alkyl,(heterocyclyl)alkyl and (heteroaryl)alkyl; optionally wherein two orthree carbon atoms of the (C₁-C₆)alkyl, (C₂-C₆)alkenyl or (C₂-C₆)alkynylform part of a 3-7-membered carbocyclic or heterocyclic ring (such as acyclobutyl or oxirane ring);

R₃ is hydrogen —CO-[Aaa], —CONR₇R₈, (C₁-C₆)alkyl, (C₂-C₆)alkenyl or(C₂-C₆)alkynyl; wherein (C₁-C₆)alkyl, (C₂-C₆)alkenyl and (C₂-C₆)alkynylare substituted by one or more substituents selected from amino,alkylamino, acylamino, —COO-alkyl, cycloalkyl, heterocyclyl, heteroaryl,guanidino, (cycloalkyl)alkyl, (heterocyclyl)alkyl and (heteroaryl)alkyl;optionally wherein two or three carbon atoms of the (C₁-C₆)alkyl,(C₂-C₆)alkenyl or (C₂-C₆)alkynyl form part of a 3-7-membered carbocyclicor heterocyclic ring (such as a cyclobutyl or oxirane ring);

R₄ and R₅ independently are hydrogen or absent;

R₆ is hydrogen, alkyl or acyl;

R₇ and R₈ independently are hydrogen, (C₁-C₆)alkyl, (C₂-C₆)alkenyl or(C₂-C₆)alkynyl; wherein (C₁-C₆)alkyl, (C₂-C₆)alkenyl and (C₂-C₆)alkynylare substituted by one or more substituents selected from halogen,hydroxyl, amino, nitro, cyano, cycloalkyl, heterocyclyl, heteroaryl,guanidino, (cycloalkyl)alkyl, (heterocyclyl)alkyl and (heteroaryl)alkyl;optionally wherein two or three carbon atoms of the (C₁-C₆)alkyl,(C₂-C₆)alkenyl or (C₂-C₆)alkynyl form part of a 3-7-membered carbocyclicor heterocyclic ring (such as a cyclobutyl or oxirane ring);

alternatively R₇ and R₈ together with the nitrogen to which they areattached form an optionally substituted 3-7-membered ring containing 0-2additional heteroatoms independently selected from N, O and S in anystable combination; wherein the optional substituent at each occurrenceis selected from hydroxyl, —COOH, —COO-alkyl, amide, halo, amino, nitroor cyano;

[Aaa] is an amino acid residue;

R_(a) is hydrogen or alkyl;

R_(b) is hydrogen or alkyl;

or R_(b) and R₂, together with the atoms to which they are attached, mayform pyrrolidine or piperidine optionally substituted with one or moregroups independently selected from hydroxyl, halo, amino, cyano andalkyl; and

with a proviso that R₁ is not the side chain of Ser, Thr, Lys, Arg orHis, when R₂ is the side chain of Asp, Asn, Glu or Gln, R₃ is hydrogen,—CO-Ser or —CO-Thr and R_(a) and R_(b) are hydrogen.

In certain preferred embodiments of Formula (I), X is O. In certain suchembodiments, the ring containing X is an oxadiazole ring.

In certain embodiments, R₁ or R₂ represents a side chain of an aminoacid. Alternatively, R₁ or R₂ may represent hydrogen.

In certain embodiments, R₁ and R₂ may independently represent(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl or cycloalkyl wherein(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl and cycloalkyl aresubstituted by carboxylic acid, carboxylate, carboxylic acid ester,thiocarboxylate, thioacid, —CONR₇R₈, hydroxy, cycloalkyl and aryl. Incertain such embodiments, R₁ and R₂ may independently represent(C₁-C₆)alkyl, (C₂-C₆)alkenyl or (C₂-C₆)alkynyl substituted by carboxylicacid ester, thiocarboxylate, thioacid or cycloalkyl.

In certain embodiments, R₁ is a side chain of an amino acid or hydrogen,(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl or cycloalkyl; wherein(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl and cycloalkyl areoptionally substituted by one or more substituents selected from amino,alkylamino, acylamino, carboxylic acid, carboxylate, carboxylic acidester, thiocarboxylate, thioacid, —CONR₇R₈, hydroxy, cycloalkyl,(cycloalkyl)alkyl, aryl, heterocyclyl, (heterocyclyl)alkyl, heteroaryl,(heteroaryl)alkyl, guanidino, —SH and —S(alkyl); optionally whereincycloalkyl, aryl, heterocyclyl and heteroaryl are further substituted byone or more substituents such as hydroxy, alkoxy, halo, amino, nitro,cyano or alkyl and optionally wherein two or three carbon atoms of the(C₁-C₆)alkyl, (C₂-C₆)alkenyl or (C₂-C₆)alkynyl form part of a3-7-membered carbocyclic or heterocyclic ring (such as a cyclobutyl oroxirane ring);

In certain embodiments, R₁ is (C₁-C₆)alkyl, (C₂-C₆)alkenyl or(C₂-C₆)alkynyl; wherein (C₁-C₆)alkyl, (C₂-C₆)alkenyl and (C₂-C₆)alkynylare optionally substituted by one or more substituents selected fromamino, alkylamino, acylamino, carboxylic acid, carboxylate,thiocarboxylate, thioacid, —CONR₇R₈, hydroxy, cycloalkyl, aryl,heterocyclyl, heteroaryl, guanidino, —SH and —S(alkyl).

In certain embodiments, R₁ is (C₁-C₆)alkyl, (C₂-C₆)alkenyl or(C₂-C₆)alkynyl substituted by one or more substituents selected fromamino, alkylamino, acylamino, heterocyclyl, heteroaryl and guanidino andis optionally further substituted by one or more substituents such asalkyl, alkoxy, aralkyl or aryl.

In certain embodiments, R₁ is (C₁-C₆)alkyl, (C₂-C₆)alkenyl or(C₂-C₆)alkynyl is substituted by amino, alkylamino, acylamino,heterocyclyl, heteroaryl, guanidino, (heterocyclyl)alkyl; wherein(heteroaryl)alkyl, heterocyclyl or heteroaryl contains at least onebasic nitrogen atom. A basic nitrogen atom refers to a nitrogen that isprotonated and positively charged at pH levels below its pK_(a) value.For example, the pK_(a) of the conjugate acid of the nitrogen-containingcompound is >5, preferably >7. In certain such embodiments, R₁ isoptionally further substituted by one or more substituents, such asalkyl, alkoxy, aralkyl or aryl.

In some embodiments, R₁ represents (C₁-C₆)alkyl, (C₂-C₆)alkenyl or(C₂-C₆)alkynyl substituted by one or more substituents selected fromcarboxylate, carboxylic acid, carboxylic acid ester, thiocarboxylate,thio acid, —CONR₇R₈, hydroxy, cycloalkyl, aryl, guanidino, —SH and—S(alkyl). In some such embodiments, R₁ represents (C₁-C₆)alkyl,(C₂-C₆)alkenyl or (C₂-C₆)alkynyl substituted by one or more substituentsselected from carboxylic acid ester, thiocarboxylate, thio acid orcycloalkyl.

In accordance with any of the foregoing embodiments, in certainembodiments, R₁ is (C₁-C₄)alkyl substituted by one or more substituentsselected from amino, heteroaryl or guanidino. In certain embodiments, R₁is —(CH₂)imidazolyl, —(CH₂)₃NHC(═N)—NH₂ or —(CH₂)₄NH₂.

In certain embodiments, R₂ is a side chain of an amino acid or hydrogen,(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl or cycloalkyl; wherein(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl and cycloalkyl areoptionally substituted by one or more substituents selected from amino,alkylamino, acylamino, carboxylic acid, carboxylate, carboxylic acidester, thiocarboxylate, thioacid, —CONR₇R₈, hydroxy, cycloalkyl,(cycloalkyl)alkyl, aryl, heterocyclyl, (heterocyclyl)alkyl, heteroaryl,(heteroaryl)alkyl, guanidino, —SH and —S(alkyl); optionally whereincycloalkyl, aryl, heterocyclyl and heteroaryl are further substituted byone or more substituents such as hydroxy, alkoxy, halo, amino, nitro,cyano or alkyl and optionally wherein two or three carbon atoms of the(C₁-C₆)alkyl, (C₂-C₆)alkenyl or (C₂-C₆)alkynyl form part of a3-7-membered carbocyclic or heterocyclic ring (such as a cyclobutyl oroxirane ring);

In certain embodiments, R₂ is (C₁-C₆)alkyl, (C₂-C₆)alkenyl or(C₂-C₆)alkynyl; wherein (C₁-C₆)alkyl, (C₂-C₆)alkenyl and (C₂-C₆)alkynylare optionally substituted by one or more substituents selected fromamino, alkylamino, acylamino, carboxylic acid, carboxylate,thiocarboxylate, thioacid, —CONR₇R₈, hydroxy, cycloalkyl, aryl,heterocyclyl, (heterocyclyl)alkyl, heteroaryl, (heteroaryl)alkyl,guanidino, —SH and —S(alkyl).). In some such embodiments, R₂ represents(C₁-C₆)alkyl, (C₂-C₆)alkenyl or (C₂-C₆)alkynyl substituted by one ormore substituents selected from alkylamino, acylamino, cycloalkyl and(heterocyclyl)alkyl.

In certain embodiments, R₂ is (C₁-C₆)alkyl substituted by one or moresubstituents selected from carboxylate, carboxylic acid, carboxylic acidester, thiocarboxylate, thio acid, amido, amino and heterocyclyl andoptionally further substituted by one or more substituents, such asalkyl, alkoxy, aralkyl or aryl. In certain such embodiments, R₂ furtheroptionally contains one or more double bonds or triple bonds. In certainembodiments, R₂ is (C₃-C₆)cycloalkyl substituted by one or moresubstituents selected from carboxylate, carboxylic acid,thiocarboxylate, thio acid, amido, ester, amino and heterocyclyl andadditionally optionally substituted by one or more further substituents,such as alkyl, alkoxy, aralkyl or aryl.

In accordance with any of the foregoing embodiments, in certainembodiments, R₂ is (C₁-C₄)alkyl substituted by one or more substituentsselected from carboxylate, carboxylic acid and amido. In certainembodiments, R₂ is —(CH₂)COOH, —(CH₂)₂COOH, —(CH₂)CONH₂ or —(CH₂)₂CONH₂.In such certain embodiments, R₂ is —(CH₂)₂C(O)NH₂, —CH₂C(O)NH₂,—(CH₂)₂C(O)NH(alkyl) or —CH₂C(O)NH(alkyl).

In some embodiments, R₂ represents (C₁-C₆)alkyl, (C₂-C₆)alkenyl or(C₂-C₆)alkynyl substituted by one or more substituents selected fromamino, alkylamino, acylamino, hydroxy, cycloalkyl, aryl,(heterocyclyl)alkyl, heteroaryl, (heteroaryl)alkyl, guanidino, —SH and—S(alkyl). In some such embodiments, R₂ represents (C₁-C₆)alkyl,(C₂-C₆)alkenyl or (C₂-C₆)alkynyl substituted by one or more substituentsselected from alkylamino, acylamino, cycloalkyl and (heterocyclyl)alkyl.

In certain embodiments, R₃ is hydrogen, —CO-[Aaa1]_(m), [Aaa1]_(m),[Aaa1]_(m)—CO-[Aaa1]_(m) or —S(O)_(p)-[Aaa1]_(m).

In certain embodiments, R₃ is —CO-Aaa1 and the side chain of Aaa1comprises a (C₁-C₄)alkyl group optionally substituted by one or moresubstituents selected from amino, alkylamino, acylamino, carboxylicacid, carboxylate, thiocarboxylate, thioacid, —CONR₇R₈, hydroxy,cycloalkyl, aryl, heterocyclyl, heteroaryl, guanidino, —SH, —S(alkyl);optionally wherein cycloalkyl, aryl, heterocyclyl and heteroaryl arefurther substituted by one or more substituents such as hydroxy, alkoxy,halo, amino, nitro, cyano or alkyl.

Alternatively, R₃ may represent —CO-[Aaa1]_(m), wherein m is greaterthan 1. In other embodiments, R₃ may represent [Aaa1]_(m),[Aaa1]_(m)—CO-[Aaa1]_(m) or —S(O)_(p)-[Aaa1]_(m), wherein m is aninteger from 1 to 3.

In further embodiments, the side chain of Aaa1 comprises a (C₁-C₄)alkylgroup substituted by one or more substituents selected from amino,acylamino, carboxylic acid, —CONR₇R₈, hydroxy, cycloalkyl, aryl,heteroaryl, guanidino, —SH and —S(alkyl); wherein R₇ and R₈independently are hydrogen, alkyl, aryl or heterocyclyl.

In further alternative embodiments, R₃ may represent (C₁-C₆)alkyl,(C₂-C₆)alkenyl or (C₂-C₆)alkynyl, substituted by carboxylic acid,carboxylate, thiocarboxylate, thioacid, —CONR₇R₈, hydroxy, —SH and—S(alkyl). Particularly, R₃ is CONR₇R₈; wherein R₇ and R₈ independentlyare hydrogen, (C₁-C₆)alkyl, (C₂-C₆)alkenyl or (C₂-C₆)alkynyl; wherein(C₁-C₆)alkyl, (C₂-C₆)alkenyl and (C₂-C₆)alkynyl are substituted by oneor more substituents selected from halogen, hydroxyl, amino, nitro,cyano, cycloalkyl, heterocyclyl, heteroaryl, guanidino,(cycloalkyl)alkyl, (heterocyclyl)alkyl and (heteroaryl)alkyl.

In further alternative embodiments, R₃ may represent —CONR₇R₈; whereinR₇ and R₈ independently are hydrogen, (C₁-C₆)alkyl, (C₂-C₆)alkenyl or(C₂-C₆)alkynyl; wherein (C₁-C₆)alkyl, (C₂-C₆)alkenyl and (C₂-C₆)alkynyl;optionally wherein two or three carbon atoms of the (C₁-C₆)alkyl,(C₂-C₆)alkenyl or (C₂-C₆)alkynyl form part of a 3-7-membered carbocyclicor heterocyclic ring (such as a cyclobutyl or oxirane ring);

In certain embodiments, R₃ is —COR or —SO₂R_(c) wherein R_(c) is(C₁-C₆)alkyl, cycloalkyl, aryl, heterocyclcyl or heteroaryl; wherein thesaid (C₁-C₆)alkyl, cycloalkyl, aryl, heterocyclcyl or heteroaryl isoptionally substituted by one or more substituents selected fromcarboxylic acid, hydroxyl, alkyl, alkoxy, amino, alkylamino, acylamino,carboxylic ester, cycloalkyl, heterocyclyl, heteroaryl,(cycloalkyl)alkyl, (heterocyclyl)alkyl or (heteroaryl)alkyl.

Alternatively, R₃ may represent —COR_(c), or —SO₂R_(c) wherein R_(c) is(C₁-C₆)alkyl, cycloalkyl, aryl, heterocyclcyl or heteroaryl; wherein thesaid (C₁-C₆)alkyl, aryl, heterocyclcyl or heteroaryl is optionallysubstituted by one or more substituents selected from carboxylic acid,hydroxyl, alkyl, amino or acylamino.

In further alternative embodiments, R₃ may represent (C₁-C₆)alkyl,(C₂-C₆)alkenyl or (C₂-C₆)alkynyl, substituted by carboxylic acid,carboxylate, thiocarboxylate, thioacid, —CONR₇R₈, hydroxy, —SH and—S(alkyl).

In certain embodiments, R₆ is hydrogen, alkyl, [Aaa2]n or—CO-[Aaa2]_(n). R₆ may be —CO-[Aaa2]_(n). Alternatively, R₆ may be H.

In certain embodiments, R₆ is —CO-Aaa2 and the side chain of Aaa2comprises a (C₁-C₄)alkyl group optionally substituted by one or moresubstituents selected from amino, alkylamino, acylamino, carboxylicacid, carboxylate, thiocarboxylate, thioacid, —CONR₇R₈, hydroxy,cycloalkyl, aryl, heterocyclyl, heteroaryl, guanidino, —SH, —S(alkyl);optionally wherein cycloalkyl, heterocyclyl and heteroaryl are furthersubstituted by one or more substituents such as hydroxy, alkoxy, halo,amino, nitro, cyano or alkyl.

In further embodiments, the side chain of Aaa2 comprises a (C₁-C₄)alkylgroup substituted by one or more substituents selected from amino,acylamino, carboxylic acid, —CONR₇R₈, hydroxy, cycloalkyl, aryl,heteroaryl, guanidino, —SH and —S(alkyl); wherein R₇ and R₈independently are hydrogen or alkyl.

In certain embodiments, Aaa1 or Aaa2 represents an amino acid residue,wherein the amino acid residue comprises a side chain that includes a—OH, —O-acyl, —SH, —NH₂ or NH(alkyl) moiety.

In certain embodiments, R₇ is (C₁-C₆)alkyl, (C₂-C₆)alkenyl or(C₂-C₆)alkynyl substituted by one or more substituents selected fromhalogen, hydroxyl, amino, nitro, cyano, cycloalkyl, heterocyclyl,heteroaryl, guanidino, (cycloalkyl)alkyl, (heterocyclyl)alkyl and(heteroaryl)alkyl.

In certain embodiments, R₈ is (C₁-C₆)alkyl, (C₂-C₆)alkenyl or(C₂-C₆)alkynyl substituted by one or more substituents selected fromhalogen, hydroxyl, amino, nitro, cyano, cycloalkyl, heterocyclyl,heteroaryl, guanidino, (cycloalkyl)alkyl, (heterocyclyl)alkyl and(heteroaryl)alkyl.

In certain embodiments, R_(a) is alkenyl, alkynyl, acyl, aralkyl, aryl,heteroaralkyl, heteroaryl, cycloalkyl, (cycloalkyl)alkyl, aminoalkyl,hydroxyalkyl or alkoxyalkyl.

In certain embodiments, R₁ is a side chain of an amino acid or hydrogen,(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl or cycloalkyl; wherein(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl and cycloalkyl areoptionally substituted by one or more substituents selected from amino,alkylamino, acylamino, carboxylic acid, carboxylate, carboxylic acidester, thiocarboxylate, thioacid, —CONR₇R₈, hydroxy, cycloalkyl,(cycloalkyl)alkyl, aryl, heterocyclyl, (heterocyclyl)alkyl, heteroaryl,(heteroaryl)alkyl, guanidino, —SH and —S(alkyl); optionally whereincycloalkyl, aryl, heterocyclyl and heteroaryl are further substituted byone or more substituents such as hydroxy, alkoxy, halo, amino, nitro,cyano or alkyl, and optionally wherein two or three carbon atoms of the(C₁-C₆)alkyl, (C₂-C₆)alkenyl, or (C₂-C₆)alkynyl form part of a3-7-membered carbocyclic or heterocyclic ring (such as a cyclobutyl oroxirane ring); and

R_(a) is hydrogen or alkyl, alkenyl, alkynyl, acyl, aralkyl, aryl,heteroaralkyl, heteroaryl, cycloalkyl, (cycloalkyl)alkyl, aminoalkyl,hydroxyalkyl, or alkoxyalkyl.

In certain embodiments, R_(b) is alkenyl, alkynyl, acyl, aralkyl, aryl,heteroaralkyl, heteroaryl, cycloalkyl, (cycloalkyl)alkyl, aminoalkyl,hydroxyalkyl or alkoxyalkyl. Alternatively, in certain embodiments,R_(b) and R₂, together with the atoms to which they are attached, form apyrrolidine or piperidine ring optionally substituted with one or moregroups independently selected from hydroxyl, halo, amino, cyano andalkyl.

In certain embodiments, the present invention provides compounds offormula (IA):

or a pharmaceutically acceptable salt or a stereoisomer thereof;wherein,

R₁, R₂, R₃, R₆, R_(a) and R_(b) are same as defined in formula (I).

In certain embodiments of the compound of formula (I) or formula (IA),R_(b) is H.

In further embodiments of the compound of formula (I) or formula (IA),R₃ is —CO-[Aaa1]_(m).

For example, the compounds of the present invention may have thestructure of formula (IB):

or a pharmaceutically acceptable salt or a stereoisomer thereof;wherein,

R₁, R₂, R₆, R_(a) [Aaa1] and m are same as defined in formula (I).

In certain embodiments, the present invention provides compounds offormula (IC):

or a pharmaceutically acceptable salt or a stereoisomer thereof;wherein,

R₁, R₂, [Aaa1] and m are same as defined in formula (I).

In certain embodiments, the present invention provides compounds offormula (ID):

or a pharmaceutically acceptable salt or a stereoisomer thereof;wherein,R₁, R₂, R₃, R_(a), R_(b), [Aaa2] and n are same as defined in formula(I).

In certain embodiments, the present invention provides compounds offormula (IE):

or a pharmaceutically acceptable salt or a stereoisomer thereof;wherein,R₁, R₂, R_(a), R_(b), [Aaa2] and n are same as defined in formula (I).

An amino acid residue is understood in the art to mean a carboxylicacid, substituted at the alpha, beta or gamma carbon by an amino (—NH₂)group. In the group —CO-Aaa, the amino acid residue Aaa is connected tothe carbonyl group CO via a covalent bond between the carbonyl carbonand the amino group of the amino acid residue. In preferred embodiments,the amino acid is an alpha-amino acid and the amino acid residue Aaa isconnected to the carbonyl group CO via a covalent bond between thecarbonyl carbon and the alpha-amino group of the amino acid residue.

In accordance with any of the foregoing embodiments, in certainembodiments, X is O.

In accordance with any of the foregoing embodiments, in certainembodiments of formula (I), (IA) or (ID), R₃ is hydrogen.

In accordance with one of the foregoing embodiments, in certainembodiments of formula (I), (IA) or (ID), R₃ is —CO-Aaa.

In accordance with any one of the foregoing embodiments, in certainembodiments of formula (I), (IA), (IB), (IC), (ID) or (IE), R₁ is alkylsubstituted by amino or heteroaryl. Preferably, R₁ is —(CH₂)₄NH₂.

In accordance with any of the foregoing embodiments, in certainembodiments, R₁ is side chain of an amino acid.

In accordance with any of the foregoing embodiments, in certainembodiments, R₂ is side chain of an amino acid.

In accordance with any of the foregoing embodiments, in certainembodiments, R₁ is a side chain of Lys, Tyr, Gln, Ser, Ala, Glu, Leu,Asp or His.

In accordance with any of the foregoing embodiments, in certainembodiments, R₁ is a side chain of Lys, Tyr or Gln.

In accordance with any of the foregoing embodiments, in certainembodiments, R₁ is a side chain of Tyr.

In accordance with any of the foregoing embodiments, in certainembodiments, R₁ is a side chain of Lys.

In accordance with any of the foregoing embodiments, in certainembodiments, R₁ is a side chain of Gln.

In alternative embodiments, R₁ does not represent a side chain of Ser orThr; i.e., R₁ is not —CH₂OH or —CH(CH₃)OH. In further alternativeembodiments, R₁ is not a side chain of Ser or Thr that is alkylated oracylated. For example, in certain embodiments, R₁ is not —CH₂OCH₃,—CH₂OAc, —CH(CH₃)OCH₃ or —CH(CH₃)OAc. In further embodiments, R₁ doesnot represent a side chain of Ser or Thr that is optionally alkylated oracylated, i.e., R₁ is not —CH₂OH, —CH(CH₃)OH, —CH₂OCH₃, —CH₂OAc,—CH(CH₃)OCH₃ or —CH(CH₃)OAc.

In accordance with any one of the foregoing embodiments, in certainembodiments of formula (I), (IA), (IB), (IC), (ID) or (IE), R₂ is alkylsubstituted by amido. In certain embodiments, R₂ is —(CH₂)₂C(O)NH₂ or—CH₂C(O)NH₂. Preferably, R₂ is —CH₂C(O)NH₂.

In accordance with any of the foregoing embodiments, in certainembodiments, R₂ is a side chain of Gly, Gln, Glu, Ser, Asn, Asp, Ala orIle.

In accordance with any of the foregoing embodiments, in certainembodiments, R₂ is a side chain of Gln, Glu, Asn, Asp or Ile.

In accordance with any of the foregoing embodiments, in certainembodiments, R₂ is a side chain of Ile.

In accordance with any of the foregoing embodiments, in certainembodiments, R₂ is a side chain of Ala.

In accordance with any of the foregoing embodiments, in certainembodiments, R₂ is a side chain of Asn.

In alternative embodiments, R₂ does not represent a side chain of Asn,Asp, Gln, or Glu; i.e., R₂ is not —CH₂C(O)NH₂, —CH₂C(O)OH,—CH₂CH₂C(O)NH₂ or —CH₂CH₂C(O)OH.

In accordance with any of the foregoing embodiments, in certainembodiments, R_(b) and R₂, together with the atoms to which they areattached, may form pyrrolidine optionally substituted with hydroxyl.

In accordance with any of the foregoing embodiments, in certainembodiments, m is 1.

In accordance with any one of the foregoing embodiments, in certainembodiments [Aaa1] comprises a side chain that includes an —OH moiety.

In accordance with any of the foregoing embodiments, in certainembodiments, [Aaa1] is Ala, Thr, Ile, Glu, Lys, Asp, Tyr, Gln, Ser orPhe.

In accordance with any of the foregoing embodiments, in certainembodiments, [Aaa1] is Ser, Thr, Tyr, Glu, Ala or Ile.

In accordance with any of the foregoing embodiments, in certainembodiments, [Aaa1] is Tyr.

In accordance with any of the foregoing embodiments, in certainembodiments, [Aaa1] is Glu.

In accordance with any of the foregoing embodiments, in certainembodiments, [Aaa1] is Ala.

In accordance with any of the foregoing embodiments, in certainembodiments, [Aaa1] is Thr.

In accordance with any of the foregoing embodiments, in certainembodiments, [Aaa1] is Ile.

In alternative embodiments, R₃ is —CO-[Aaa1], and Aaa1 does notrepresent an amino acid residue of Thr or Ser.

In further alternative embodiments, R₃ is not H or —CO-[Aaa1].

In accordance with any of the foregoing embodiments, in certainembodiments, n is 1.

In accordance with any of the foregoing embodiments, in certainembodiments, [Aaa2] is Ala, Thr, Ile, Glu, Lys, Asp, Tyr, Gln, Ser orPhe.

In accordance with any of the foregoing embodiments, in certainembodiments, [Aaa2] is Ser, Thr, Tyr, Glu, Ala or Ile.

In accordance with any of the foregoing embodiments, in certainembodiments, p is 2.

In accordance with any of the foregoing embodiments, in certainembodiments, one, more or all amino acid residues are D amino acidresidues.

In accordance with any of the foregoing embodiments, in certainembodiments, one, more than one or all amino acid residues are L aminoacid residues.

In certain embodiments, the present invention provides a compound or apharmaceutically acceptable salt or a stereoisomer thereof, selectedfrom:

Compound No. Structure 1

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or a pharmaceutically acceptable salt thereof or a stereoisomer thereof.

In certain embodiments, compounds of the invention may be prodrugs ofthe compounds of formula (I), e.g., wherein a hydroxyl in the parentcompound is presented as an ester or a carbonate or carboxylic acidpresent in the parent compound is presented as an ester. In a furtherembodiment, the prodrug is metabolized to the active parent compound invivo (e.g., the ester is hydrolyzed to the corresponding hydroxyl orcarboxylic acid).

In certain embodiments, the compounds of the present invention can alsocontain unnatural proportions of atomic isotopes at one or more of theatoms that constitute such compounds. For example, the present inventionalso embraces isotopically-labeled variants of the present inventionwhich are identical to those recited herein, but for the fact that oneor more atoms of the compound are replaced by an atom having the atomicmass or mass number different from the predominant atomic mass or massnumber usually found in nature for the atom. All isotopes of anyparticular atom or element as specified are contemplated within thescope of the compounds of the invention and their uses. Exemplaryisotopes that can be incorporated in to compounds of the inventioninclude isotopes of hydrogen, carbon, nitrogen, oxygen, phosphorous,sulfur, fluorine, chlorine and iodine, such as ²H (“D”), ³H, ¹¹C, ¹³C,¹⁴C, ¹³N, ¹⁵N, ¹⁵O, ¹⁷O, ¹⁸O, ³⁵S, ¹⁸F, ³⁶Cl, ¹²³I and ¹²⁵I.Isotopically labeled compounds of the present inventions can generallybe prepared by following procedures analogous to those disclosed in theschemes and/or in the examples herein below, by substituting anisotopically labeled reagent for a non-isotopically labeled reagent.

Pharmaceutical Compositions

In certain embodiments, the present invention provides a pharmaceuticalcomposition comprising a compound as disclosed herein, optionallyadmixed with a pharmaceutically acceptable carrier or diluent.

The present invention also provides methods for formulating thedisclosed compounds for pharmaceutical administration.

The compositions and methods of the present invention may be utilized totreat an individual in need thereof. In certain embodiments, theindividual is a mammal such as a human or a non-human mammal. Whenadministered to an animal, such as a human, the composition or thecompound is preferably administered as a pharmaceutical compositioncomprising, for example, a compound of the invention and apharmaceutically acceptable carrier. Pharmaceutically acceptablecarriers are well known in the art and include, for example, aqueoussolutions such as water or physiologically buffered saline or othersolvents or vehicles such as glycols, glycerol, oils such as olive oilor injectable organic esters. In a preferred embodiment, when suchpharmaceutical compositions are for human administration, particularlyfor invasive routes of administration (i.e., routes, such as injectionor implantation, that circumvent transport or diffusion through anepithelial barrier), the aqueous solution is pyrogen-free orsubstantially pyrogen-free. The excipients can be chosen, for example,to effect delayed release of an agent or to selectively target one ormore cells, tissues or organs. The pharmaceutical composition can be indosage unit form such as tablet, capsule (including sprinkle capsule andgelatin capsule), granule, lyophile for reconstitution, powder,solution, syrup, suppository, injection or the like. The composition canalso be present in a transdermal delivery system, e.g., a skin patch.The composition can also be present in a solution suitable for topicaladministration, such as an eye drop.

A pharmaceutically acceptable carrier can contain physiologicallyacceptable agents that act, for example, to stabilize, increasesolubility or to increase the absorption of a compound such as acompound of the invention. Such physiologically acceptable agentsinclude, for example, carbohydrates, such as glucose, sucrose ordextrans, antioxidants, such as ascorbic acid or glutathione, chelatingagents, low molecular weight proteins or other stabilizers orexcipients. The choice of a pharmaceutically acceptable carrier,including a physiologically acceptable agent, depends, for example, onthe route of administration of the composition. The preparation ofpharmaceutical composition can be a self-emulsifying drug deliverysystem or a self-microemulsifying drug delivery system. Thepharmaceutical composition (preparation) also can be a liposome or otherpolymer matrix, which can have incorporated therein, for example, acompound of the invention. Liposomes, for example, which comprisephospholipids or other lipids, are nontoxic, physiologically acceptableand metabolizable carriers that are relatively simple to make andadminister.

The phrase “pharmaceutically acceptable” is employed herein to refer tothose compounds, materials, compositions and/or dosage forms which are,within the scope of sound medical judgment, suitable for use in contactwith the tissues of human beings and animals without excessive toxicity,irritation, allergic response or other problem or complication,commensurate with a reasonable benefit/risk ratio.

The phrase “pharmaceutically acceptable carrier” as used herein means apharmaceutically acceptable material, composition or vehicle, such as aliquid or solid filler, diluent, excipient, solvent or encapsulatingmaterial. Each carrier must be “acceptable” in the sense of beingcompatible with the other ingredients of the formulation and notinjurious to the patient. Some examples of materials which can serve aspharmaceutically acceptable carriers include: (1) sugars, such aslactose, glucose and sucrose; (2) starches, such as corn starch andpotato starch; (3) cellulose and its derivatives, such as sodiumcarboxymethyl cellulose, ethyl cellulose and cellulose acetate; (4)powdered tragacanth; (5) malt; (6) gelatin; (7) talc; (8) excipients,such as cocoa butter and suppository waxes; (9) oils, such as peanutoil, cottonseed oil, safflower oil, sesame oil, olive oil, corn oil andsoybean oil; (10) glycols, such as propylene glycol; (11) polyols, suchas glycerin, sorbitol, mannitol and polyethylene glycol; (12) esters,such as ethyl oleate and ethyl laurate; (13) agar; (14) bufferingagents, such as magnesium hydroxide and aluminum hydroxide; (15) alginicacid; (16) pyrogen-free water; (17) isotonic saline; (18) Ringer'ssolution; (19) ethyl alcohol; (20) phosphate buffer solutions; and (21)other non-toxic compatible substances employed in pharmaceuticalformulations.

A pharmaceutical composition (preparation) can be administered to asubject by any of a number of routes of administration including, forexample orally (for example, drenches as in aqueous or non-aqueoussolutions or suspensions, tablets, capsules (including sprinkle capsulesand gelatin capsules), boluses, powders, granules, pastes forapplication to the tongue); absorption through the oral mucosa (e.g.,sublingually); anally, rectally or vaginally (for example, as a pessary,cream or foam); parenterally (including intramuscularly, intravenously,subcutaneously or intrathecally as, for example, a sterile solution orsuspension); nasally; intraperitoneally; subcutaneously; transdermally(for example as a patch applied to the skin); and topically (forexample, as a cream, ointment or spray applied to the skin or as an eyedrop). The compound may also be formulated for inhalation. In certainembodiments, a compound may be simply dissolved or suspended in sterilewater. Details of appropriate routes of administration and compositionssuitable for same can be found in, for example, U.S. Pat. Nos.6,110,973, 5,763,493, 5,731,000, 5,541,231, 5,427,798, 5,358,970 and4,172,896, as well as in patents cited therein.

The formulations may conveniently be presented in unit dosage form andmay be prepared by any methods well known in the art of pharmacy. Theamount of active ingredient which can be combined with a carriermaterial to produce a single dosage form will vary depending upon thehost being treated, the particular mode of administration. The amount ofactive ingredient that can be combined with a carrier material toproduce a single dosage form will generally be that amount of thecompound which produces a therapeutic effect. Generally, out of onehundred percent, this amount will range from about 1 percent to aboutninety-nine percent of active ingredient, preferably from about 5percent to about 70 percent, most preferably from about 10 percent toabout 30 percent.

Methods of preparing these formulations or compositions include the stepof bringing into association an active compound, such as a compound ofthe invention, with the carrier and, optionally, one or more accessoryingredients. In general, the formulations are prepared by uniformly andintimately bringing into association a compound of the present inventionwith liquid carriers or finely divided solid carriers or both and then,if necessary, shaping the product.

Formulations of the invention suitable for oral administration may be inthe form of capsules (including sprinkle capsules and gelatin capsules),cachets, pills, tablets, lozenges (using a flavored basis, usuallysucrose and acacia or tragacanth), lyophile, powders, granules or as asolution or a suspension in an aqueous or non-aqueous liquid or as anoil-in-water or water-in-oil liquid emulsion or as an elixir or syrup oras pastilles (using an inert base, such as gelatin and glycerin orsucrose and acacia) and/or as mouth washes and the like, each containinga predetermined amount of a compound of the present invention as anactive ingredient. Compositions or compounds may also be administered asa bolus, electuary or paste.

To prepare solid dosage forms for oral administration (capsules(including sprinkle capsules and gelatin capsules), tablets, pills,dragees, powders, granules and the like), the active ingredient is mixedwith one or more pharmaceutically acceptable carriers, such as sodiumcitrate or dicalcium phosphate and/or any of the following: (1) fillersor extenders, such as starches, lactose, sucrose, glucose, mannitoland/or silicic acid; (2) binders, such as, for example,carboxymethylcellulose, alginates, gelatin, polyvinyl pyrrolidone,sucrose and/or acacia; (3) humectants, such as glycerol; (4)disintegrating agents, such as agar-agar, calcium carbonate, potato ortapioca starch, alginic acid, certain silicates and sodium carbonate;(5) solution retarding agents, such as paraffin; (6) absorptionaccelerators, such as quaternary ammonium compounds; (7) wetting agents,such as, for example, cetyl alcohol and glycerol monostearate; (8)absorbents, such as kaolin and bentonite clay; (9) lubricants, such atalc, calcium stearate, magnesium stearate, solid polyethylene glycols,sodium lauryl sulfate and mixtures thereof; (10) complexing agents, suchas, modified and unmodified cyclodextrins; and (11) coloring agents. Inthe case of capsules (including sprinkle capsules and gelatin capsules),tablets and pills, the pharmaceutical compositions may also comprisebuffering agents. Solid compositions of a similar type may also beemployed as fillers in soft and hard-filled gelatin capsules using suchexcipients as lactose or milk sugars, as well as high molecular weightpolyethylene glycols and the like.

A tablet may be made by compression or molding, optionally with one ormore accessory ingredients. Compressed tablets may be prepared usingbinder (for example, gelatin or hydroxypropylmethyl cellulose),lubricant, inert diluent, preservative, disintegrant (for example,sodium starch glycolate or cross-linked sodium carboxymethyl cellulose),surface-active or dispersing agent. Molded tablets may be made bymolding in a suitable machine a mixture of the powdered compoundmoistened with an inert liquid diluent.

The tablets and other solid dosage forms of the pharmaceuticalcompositions, such as dragees, capsules (including sprinkle capsules andgelatin capsules), pills and granules, may optionally be scored orprepared with coatings and shells, such as enteric coatings and othercoatings well known in the pharmaceutical-formulating art. They may alsobe formulated so as to provide slow or controlled release of the activeingredient therein using, for example, hydroxypropylmethyl cellulose invarying proportions to provide the desired release profile, otherpolymer matrices, liposomes and/or microspheres. They may be sterilizedby, for example, filtration through a bacteria-retaining filter or byincorporating sterilizing agents in the form of sterile solidcompositions that can be dissolved in sterile water or some othersterile injectable medium immediately before use. These compositions mayalso optionally contain opacifying agents and may be of a compositionthat they release the active ingredient(s) only or preferentially, in acertain portion of the gastrointestinal tract, optionally, in a delayedmanner. Examples of embedding compositions that can be used includepolymeric substances and waxes. The active ingredient can also be inmicroencapsulated form, if appropriate, with one or more of theabove-described excipients.

Liquid dosage forms useful for oral administration includepharmaceutically acceptable emulsions, lyophiles for reconstitution,microemulsions, solutions, suspensions, syrups and elixirs. In additionto the active ingredient, the liquid dosage forms may contain inertdiluents commonly used in the art, such as, for example, water or othersolvents, cyclodextrins and derivatives thereof, solubilizing agents andemulsifiers, such as ethyl alcohol, isopropyl alcohol, ethyl carbonate,ethyl acetate, benzyl alcohol, benzyl benzoate, propylene glycol,1,3-butylene glycol, oils (in particular, cottonseed, groundnut, corn,germ, olive, castor and sesame oils), glycerol, tetrahydrofuryl alcohol,polyethylene glycols and fatty acid esters of sorbitan and mixturesthereof.

Besides inert diluents, the oral compositions can also include adjuvantssuch as wetting agents, emulsifying and suspending agents, sweetening,flavoring, coloring, perfuming and preservative agents.

Suspensions, in addition to the active compounds, may contain suspendingagents as, for example, ethoxylated isostearyl alcohols, polyoxyethylenesorbitol and sorbitan esters, microcrystalline cellulose, aluminummetahydroxide, bentonite, agar-agar and tragacanth and mixtures thereof.

Formulations of the pharmaceutical compositions for rectal, vaginal orurethral administration may be presented as a suppository, which may beprepared by mixing one or more active compounds with one or moresuitable nonirritating excipients or carriers comprising, for example,cocoa butter, polyethylene glycol, a suppository wax or a salicylate andwhich is solid at room temperature, but liquid at body temperature and,therefore, will melt in the rectum or vaginal cavity and release theactive compound.

Formulations of the pharmaceutical compositions for administration tothe mouth may be presented as a mouthwash or an oral spray or an oralointment.

Alternatively or additionally, compositions can be formulated fordelivery via a catheter, stent, wire or other intraluminal device.Delivery via such devices may be especially useful for delivery to thebladder, urethra, ureter, rectum or intestine.

Formulations which are suitable for vaginal administration also includepessaries, tampons, creams, gels, pastes, foams or spray formulationscontaining such carriers as are known in the art to be appropriate.

Dosage forms for the topical or transdermal administration includepowders, sprays, ointments, pastes, creams, lotions, gels, solutions,patches and inhalants. The active compound may be mixed under sterileconditions with a pharmaceutically acceptable carrier and with anypreservatives, buffers or propellants that may be required.

The ointments, pastes, creams and gels may contain, in addition to anactive compound, excipients, such as animal and vegetable fats, oils,waxes, paraffins, starch, tragacanth, cellulose derivatives,polyethylene glycols, silicones, bentonites, silicic acid, talc and zincoxide or mixtures thereof.

Powders and sprays can contain, in addition to an active compound,excipients such as lactose, talc, silicic acid, aluminum hydroxide,calcium silicates and polyamide powder or mixtures of these substances.Sprays can additionally contain customary propellants, such aschlorofluorohydrocarbons and volatile unsubstituted hydrocarbons, suchas butane and propane.

Transdermal patches have the added advantage of providing controlleddelivery of a compound of the present invention to the body. Such dosageforms can be made by dissolving or dispersing the active compound in theproper medium. Absorption enhancers can also be used to increase theflux of the compound across the skin. The rate of such flux can becontrolled by either providing a rate controlling membrane or dispersingthe compound in a polymer matrix or gel.

Ophthalmic formulations, eye ointments, powders, solutions and the like,are also contemplated as being within the scope of this invention.Exemplary ophthalmic formulations are described in U.S. Publication Nos.2005/0080056, 2005/0059744, 2005/0031697 and 2005/004074 and U.S. Pat.No. 6,583,124, the contents of which are incorporated herein byreference. If desired, liquid ophthalmic formulations have propertiessimilar to that of lacrimal fluids, aqueous humor or vitreous humor orare compatable with such fluids. A preferred route of administration islocal administration (e.g., topical administration, such as eye drops oradministration via an implant).

The phrases “parenteral administration” and “administered parenterally”as used herein means modes of administration other than enteral andtopical administration, usually by injection and includes, withoutlimitation, intravenous, intramuscular, intraarterial, intrathecal,intracapsular, intraorbital, intracardiac, intradermal, intraperitoneal,transtracheal, subcutaneous, subcuticular, intraarticular, subcapsular,subarachnoid, intraspinal and intrasternal injection and infusion.

Pharmaceutical compositions suitable for parenteral administrationcomprise one or more active compounds in combination with one or morepharmaceutically acceptable sterile isotonic aqueous or nonaqueoussolutions, dispersions, suspensions or emulsions or sterile powderswhich may be reconstituted into sterile injectable solutions ordispersions just prior to use, which may contain antioxidants, buffers,bacteriostats, solutes which render the formulation isotonic with theblood of the intended recipient or suspending or thickening agents.

Examples of suitable aqueous and nonaqueous carriers that may beemployed in the pharmaceutical compositions of the invention includewater, ethanol, polyols (such as glycerol, propylene glycol,polyethylene glycol and the like) and suitable mixtures thereof,vegetable oils, such as olive oil and injectable organic esters, such asethyl oleate. Proper fluidity can be maintained, for example, by the useof coating materials, such as lecithin, by the maintenance of therequired particle size in the case of dispersions and by the use ofsurfactants.

These compositions may also contain adjuvants such as preservatives,wetting agents, emulsifying agents and dispersing agents. Prevention ofthe action of microorganisms may be ensured by the inclusion of variousantibacterial and antifungal agents, for example, paraben,chlorobutanol, phenol sorbic acid and the like. It may also be desirableto include isotonic agents, such as sugars, sodium chloride and the likeinto the compositions. In addition, prolonged absorption of theinjectable pharmaceutical form may be brought about by the inclusion ofagents that delay absorption such as aluminum monostearate and gelatin.

In some cases, in order to prolong the effect of a drug, it is desirableto slow the absorption of the drug from subcutaneous or intramuscularinjection. This may be accomplished by the use of a liquid suspension ofcrystalline or amorphous material having poor water solubility. The rateof absorption of the drug then depends upon its rate of dissolution,which, in turn, may depend upon crystal size and crystalline form.Alternatively, delayed absorption of a parenterally administered drugform is accomplished by dissolving or suspending the drug in an oilvehicle.

Injectable depot forms are made by forming microencapsulated matrices ofthe subject compounds in biodegradable polymers such aspolylactide-polyglycolide. Depending on the ratio of drug to polymer andthe nature of the particular polymer employed, the rate of drug releasecan be controlled. Examples of other biodegradable polymers includepoly(orthoesters) and poly(anhydrides). Depot injectable formulationsare also prepared by entrapping the drug in liposomes or microemulsionsthat are compatible with body tissue.

For use in the methods of this invention, active compounds can be givenper se or as a pharmaceutical composition containing, for example, 0.1to 99.5% (more preferably, 0.5 to 90%) of active ingredient incombination with a pharmaceutically acceptable carrier.

Methods of introduction may also be provided by rechargeable orbiodegradable devices. Various slow release polymeric devices have beendeveloped and tested in vivo in recent years for the controlled deliveryof drugs, including proteinaceous biopharmaceuticals. A variety ofbiocompatible polymers (including hydrogels), including bothbiodegradable and non-degradable polymers, can be used to form animplant for the sustained release of a compound at a particular targetsite.

Actual dosage levels of the active ingredients in the pharmaceuticalcompositions may be varied so as to obtain an amount of the activeingredient that is effective to achieve the desired therapeutic responsefor a particular patient, composition and mode of administration,without being toxic to the patient.

The selected dosage level will depend upon a variety of factorsincluding the activity of the particular compound or combination ofcompounds employed or the ester, salt or amide thereof, the route ofadministration, the time of administration, the rate of excretion of theparticular compound(s) being employed, the duration of the treatment,other drugs, compounds and/or materials used in combination with theparticular compound(s) employed, the age, sex, weight, condition,general health and prior medical history of the patient being treatedand like factors well known in the medical arts.

A physician or veterinarian having ordinary skill in the art can readilydetermine and prescribe the therapeutically effective amount of thepharmaceutical composition required. For example, the physician orveterinarian could start doses of the pharmaceutical composition orcompound at levels lower than that required in order to achieve thedesired therapeutic effect and gradually increase the dosage until thedesired effect is achieved. By “therapeutically effective amount” ismeant the concentration of a compound that is sufficient to elicit thedesired therapeutic effect. It is generally understood that theeffective amount of the compound will vary according to the weight, sex,age and medical history of the subject.

Other factors which influence the effective amount may include, but arenot limited to, the severity of the patient's condition, the disorderbeing treated, the stability of the compound and, if desired, anothertype of therapeutic agent being administered with the compound of theinvention. A larger total dose can be delivered by multipleadministrations of the agent. Methods to determine efficacy and dosageare known to those skilled in the art (Isselbacher et al. (1996)Harrison's Principles of Internal Medicine 13 ed., 1814-1882, hereinincorporated by reference).

In general, a suitable daily dose of an active compound used in thecompositions and methods of the invention will be that amount of thecompound that is the lowest dose effective to produce a therapeuticeffect. Such an effective dose will generally depend upon the factorsdescribed above.

If desired, the effective daily dose of the active compound may beadministered as one, two, three, four, five, six or more sub-dosesadministered separately at appropriate intervals throughout the day,optionally, in unit dosage forms. In certain embodiments of the presentinvention, the active compound may be administered two or three timesdaily. In preferred embodiments, the active compound will beadministered once daily.

The patient receiving this treatment is any animal in need, includingprimates, in particular humans and other mammals such as equines,cattle, swine and sheep; and poultry and pets in general.

Wetting agents, emulsifiers and lubricants, such as sodium laurylsulfate and magnesium stearate, as well as coloring agents, releaseagents, coating agents, sweetening, flavoring and perfuming agents,preservatives and antioxidants can also be present in the compositions.

Examples of pharmaceutically acceptable antioxidants include: (1)water-soluble antioxidants, such as ascorbic acid, cysteinehydrochloride, sodium bisulfate, sodium metabisulfite, sodium sulfiteand the like; (2) oil-soluble antioxidants, such as ascorbyl palmitate,butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT),lecithin, propyl gallate, alpha-tocopherol and the like; and (3)metal-chelating agents, such as citric acid, ethylenediamine tetraaceticacid (EDTA), sorbitol, tartaric acid, phosphoric acid and the like.

Methods of Treatment

The programmed cell death protein 1 pathway (PD-1) pathway has beenimplicated in a number of diseases and conditions and the pathway isknown to regulate various immune responses. Numerous studies have soughtto activate immune response by targeting the PD-1 pathway, therebyproviding a therapy for certain conditions, such as cancers. In fact,studies indicate that blockade of the PD-1 pathway, for example byinhibiting an immunosuppressive signal induced by PD-1, PD-LI or PD-L2,leads to anti-tumor activity in various cancers, including lung, breast,colon, renal, bladder, thyroid, prostate, osteosarcoma and Hodgkin'slymphoma.

Furthermore, PD-1 activity has also been associated with autoimmuneconditions, such as lupus erythematosus, juvenile idiopathic arthritisand allergic encephalomyelitis.

In certain embodiments, the present invention provides uses of acompound of the present invention for the preparation of a medicament,e.g., for the treatment of cancer.

In certain embodiments, the present invention provides methods fortreating cancer, wherein the method comprises administration of atherapeutically effective amount of a compound of the present inventionto the subject in need thereof.

In certain embodiments, the present invention provides methods forinhibiting growth of tumour cells and/or metastasis by administering atherapeutically effective amount of compounds of the present inventionto the subject in need thereof.

In certain embodiments, the present invention provides methods forinhibiting growth of tumour cells and/or metastasis by administering atherapeutically effective amount of compound of formula (I) to thesubject in need thereof.

In certain embodiments, the present invention provides methods fortreating cancer, by administering a therapeutically effective amount ofcompound of formula (I) to the subject in need thereof.

Representative tumour cells include cells of a cancer such as but arenot limited to melanoma, renal cancer, prostate cancer, breast cancer,colon cancer and lung cancer, bone cancer, pancreatic cancer, skincancer, cancer of the head or neck, cutaneous or intraocular malignantmelanoma, uterine cancer, ovarian cancer, rectal cancer, cancer of theanal region, stomach cancer, testicular cancer, carcinoma of thefallopian tubes, carcinoma of the endometrium, carcinoma of the cervix,carcinoma of the vagina, carcinoma of the vulva, Hodgkin's Disease,non-Hodgkin's lymphoma, cancer of the esophagus, cancer of the smallintestine, cancer of the endocrine system, cancer of the thyroid gland,cancer of the parathyroid gland, cancer of the adrenal gland, sarcoma ofsoft tissue, cancer of the urethra, cancer of the penis, chronic oracute leukemias including acute myeloid leukemia, chronic myeloidleukemia, acute lymphoblastic leukemia, chronic lymphocytic leukemia,solid tumours of childhood, lymphocytic lymphoma, cancer of the bladder,cancer of the kidney or ureter, carcinoma of the renal pelvis, neoplasmof the central nervous system (CNS), non-small cell lung cancer (NSCLC),primary CNS lymphoma, tumour angiogenesis, spinal axis tumour, brainstem glioma, pituitary adenoma, Kaposi's sarcoma, epidermoid cancer,squamous cell cancer, T-cell lymphoma, environmentally induced cancersincluding those induced by asbestos and combinations of said cancers.

In certain embodiments, the present invention provides methods fortreating cancer, wherein the cancer is selected from lung cancer, breastcancer, colon cancer, renal cancer, bladder cancer, thyroid cancer,prostate cancer, osteosarcoma and Hodgkin's lymphoma.

In certain embodiments, the present invention provides methods fortreating bacterial, viral or fungal infection or an immunologicalcondition, by administering a therapeutically effective amount ofcompound of formula (I) or a pharmaceutically acceptable salt thereofand a stereoisomer thereof to the subject in need thereof.

In certain embodiments, the present invention provides uses of acompound of the present invention for the preparation of a medicamentfor the treatment of bacterial, viral and fungal infection, as well asmethods of administering a therapeutically effective amount of acompound of the present invention for the treatment of a bacterial,viral or fungal infection.

In certain embodiments, the present invention provides uses of acompound of formula (I) for the preparation of a medicament for thetreatment of bacterial, viral and fungal infection, as well as methodsof administering a therapeutically effective amount of compound offormula (I) or a pharmaceutically acceptable salt thereof and astereoisomer thereof for the treatment of a bacterial, viral or fungalinfection.

Still yet other embodiments of the present invention provides a methodof treatment of infection by blockade of the PD-1 pathway, for exampleinhibiting an immunosuppressive signal induced by PD-1, PD-L1 or PD-L2,wherein the method comprises administration of a therapeuticallyeffective amount of a compound of the present invention to the subjectin need thereof.

In certain embodiments, the invention provides uses of a compound of thepresent invention in inhibiting the PD-1 pathway (e.g., PD-1, PD-L1 orPD-L2).

In certain embodiments, the present invention provides methods fortreating infectious disease in a subject comprising administering atherapeutically effective amount of a compound of the present inventionfor the treatment of the infectious disease.

In certain embodiments, the present invention provides compound offormula (I) or a pharmaceutically acceptable salt thereof and astereoisomer thereof for use as a medicament.

In certain embodiments, the present invention provides compound offormula (I) or a pharmaceutically acceptable salt thereof and astereoisomer thereof for use in the treatment of cancer.

In certain embodiments, the present invention provides compound offormula (I) or a pharmaceutically acceptable salt thereof and astereoisomer thereof for use in the treatment of lung cancer, breastcancer, colon cancer, renal cancer, bladder cancer, thyroid cancer,prostate cancer, osteosarcoma and Hodgkin's lymphoma.

In certain embodiments, the present invention provides compound offormula (I) or a pharmaceutically acceptable salt thereof and astereoisomer thereof for use in the treatment of bacterial, viral orfungal infection or an immunological condition.

Representative infectious disease include but are not limited to HIV,Influenza, Herpes, Giardia, Malaria, Leishmania, the pathogenicinfection by the virus Hepatitis (A, B, & C), herpes virus (e.g., VZV,HSV-1, HAV-6, HSV-II and CMV, Epstein Barr virus), adenovirus, influenzavirus, flaviviruses, echovirus, rhinovirus, coxsackie virus, cornovirus,respiratory syncytial virus, mumps virus, rotavirus, measles virus,rubella virus, parvovirus, vaccinia virus, HTLV virus, dengue virus,papillomavirus, molluscum virus, poliovirus, rabies virus, JC virus andarboviral encephalitis virus, pathogenic infection by the bacteriachlamydia, rickettsial bacteria, mycobacteria, staphylococci,streptococci, pneumonococci, meningococci and conococci, klebsiella,proteus, serratia, pseudomonas, E. coli, legionella, diphtheria,salmonella, bacilli, cholera, tetanus, botulism, anthrax, plague,leptospirosis and Lyme's disease bacteria, pathogenic infection by thefungi Candida (albicans, krusei, glabrata, tropicalis, etc.),Cryptococcus neoformans, Aspergillus (fumigatus, niger, etc.), GenusMucorales (mucor, absidia, rhizophus), Sporothrix schenkii, Blastomycesdermatitidis, Paracoccidioides brasiliensis, Coccidioides immitis andHistoplasma capsulatum and pathogenic infection by the parasitesEntamoeba histolytica, Balantidium coli, Naegleriafowleri, Acanthamoebasp., Giardia lambia, Cryptosporidium sp., Pneumocystis carinii,Plasmodium vivax, Babesia microti, Trypanosoma brucei, Trypanosomacruzi, Leishmania donovani, Toxoplasma gondi, Nippostrongylusbrasiliensis.

The compounds of the present invention may be used as single drugs(monotherapy) or conjointly with one or more other agents (conjointtherapy). The compounds may be used by themselves or, preferably, in apharmaceutical composition in which the compound is mixed with one ormore pharmaceutically acceptable materials.

The pharmaceutical composition may be administered by oral or inhalationroutes or by parenteral administration route. For example, compositionscan be administered orally, by intravenous infusion, topically,intraperitoneally, intravesically or intrathecally. Examples ofparenteral administration includes but are not limited to intraarticular(in the joints), intravenous, intramuscular, intradermal,intraperitoneal and subcutaneous routes. Suitable liquid compositionsmay be aqueous or non-aqueous, isotonic sterile injection solutions andmay contain antioxidants, buffers, bacteriostats and solutes that renderthe formulation isotonic with the blood of the intended recipient andaqueous and non-aqueous sterile suspensions that can include suspendingagents, solubilizers, thickening agents, stabilizers and preservatives.Oral administration, parenteral administration, subcutaneousadministration and intravenous administration are preferred methods ofadministration.

The dosage of the compounds of the present invention varies depending ona patient's age, weight or symptoms, as well as the compound's potencyor therapeutic efficacy, the dosing regimen and/or treatment time.Generally, suitable routes of administration may, for example, includeoral, eyedrop, rectal, transmucosal, topical or intestinaladministration; parenteral delivery, including intramuscular,subcutaneous, intramedullary injections, as well as intrathecal, directintraventricular, intravenous, intraperitoneal, intranasal orintraocular injections. The compounds of the invention may beadministered in an amount of 0.5 mg or 1 mg up to 500 mg, 1 g or 2 g perdosage regimen.

The dosage may be administered once per week, once per three days, onceper two days, once per day, twice per day, three times per day or moreoften. In alternative embodiments, in certain adults the compound can becontinuously administered by intravenous administration for a period oftime designated by a physician. Since the dosage is affected by variousconditions, an amount less than or greater than the dosage rangescontemplated about may be implemented in certain cases. A physician canreadily determine the appropriate dosage for a patient undergoingtherapeutic treatment.

The compounds of the present invention may be administered incombination with one or more other drugs (1) to complement and/orenhance effect of the compound of the present invention, (2) to modulatepharmacodynamics, improve absorption or reduce dosage of the compound ofthe present invention and/or (3) to reduce or ameliorate the sideeffects of the compound of the present invention. As used herein, thephrase “conjoint administration” refers to any form of administration oftwo or more different therapeutic compounds such that the secondcompound is administered while the previously administered therapeuticcompound is still effective in the body (e.g., the two compounds aresimultaneously effective in the patient, which may include synergisticeffects of the two compounds). For example, the different therapeuticcompounds can be administered either in the same formulation or in aseparate formulation, either concomitantly or sequentially. In certainembodiments, the different therapeutic compounds can be administeredwithin one hour, 12 hours, 24 hours, 36 hours, 48 hours, 72 hours or aweek of one another. Thus, an individual who receives such treatment canbenefit from a combined effect of different therapeutic compounds. Therespective compounds may be administered by the same or different routeand the same or different method.

The dosage of the other drug can be a dosage that has been clinicallyused or may be a reduced dosage that is effective when administered incombination with a compound of the present invention. The ratio of thecompound of the present invention and the other drug can vary accordingto age and weight of a subject to be administered, administrationmethod, administration time, disorder to be treated, symptom andcombination thereof. For example, the other drug may be used in anamount of 0.01 to 100 parts by mass, based on 1 part by mass of thecompound of the present invention.

Conjoint therapy can be employed to treat any diseases discussed herein.For example, in the methods of the invention directed to the treatmentof cancer, the compound of the present invention can be used with anexisting chemotherapeutic conjointly using a single pharmaceuticalcomposition or a combination of different pharmaceutical compositions.Examples of the chemotherapeutic include an alkylation agent,nitrosourea agent, antimetabolite, anticancer antibiotics,vegetable-origin alkaloid, topoisomerase inhibitor, hormone drug,hormone antagonist, aromatase inhibitor, P-glycoprotein inhibitor,platinum complex derivative, other immunotherapeutic drugs and otheranticancer drugs. Further, a compound of the invention can beadministered conjointly with a cancer treatment adjunct, such as aleucopenia (neutropenia) treatment drug, thrombocytopenia treatmentdrug, antiemetic and cancer pain intervention drug, concomitantly or ina mixture form. Chemotherapeutic agents that may be conjointlyadministered with compounds of the invention include: aminoglutethimide,amsacrine, anastrozole, asparaginase, bcg, bicalutamide, bleomycin,bortezomib, buserelin, busulfan, campothecin, capecitabine, carboplatin,carfilzomib, carmustine, chlorambucil, chloroquine, cisplatin,cladribine, clodronate, colchicine, cyclophosphamide, cyproterone,cytarabine, dacarbazine, dactinomycin, daunorubicin, demethoxyviridin,dexamethasone, dichloroacetate, dienestrol, diethylstilbestrol,docetaxel, doxorubicin, epirubicin, estradiol, estramustine, etoposide,everolimus, exemestane, filgrastim, fludarabine, fludrocortisone,fluorouracil, fluoxymesterone, flutamide, gemcitabine, genistein,goserelin, hydroxyurea, idarubicin, ifosfamide, imatinib, interferon,irinotecan, ironotecan, lenalidomide, letrozole, leucovorin, leuprolide,levamisole, lomustine, lonidamine, mechlorethamine, medroxyprogesterone,megestrol, melphalan, mercaptopurine, mesna, metformin, methotrexate,mitomycin, mitotane, mitoxantrone, nilutamide, nocodazole, octreotide,oxaliplatin, paclitaxel, pamidronate, pentostatin, perifosine,plicamycin, pomalidomide, porfimer, procarbazine, raltitrexed,rituximab, sorafenib, streptozocin, sunitinib, suramin, tamoxifen,temozolomide, temsirolimus, teniposide, testosterone, thalidomide,thioguanine, thiotepa, titanocene dichloride, topotecan, trastuzumab,tretinoin, vinblastine, vincristine, vindesine and vinorelbine.

In certain embodiments, a compound of the invention may be conjointlyadministered with non-chemical methods of cancer treatment. In a furtherembodiment, a compound of the invention may be conjointly administeredwith radiation therapy. In a further embodiment, a compound of theinvention may be conjointly administered with surgery, withthermoablation, with focused ultrasound therapy, with cryotherapy orwith any combination of these.

In certain embodiments, different compounds of the invention may beconjointly administered with one or more other compounds of theinvention. Moreover, such combinations may be conjointly administeredwith other therapeutic agents, such as other agents suitable for thetreatment of cancer, immunological or neurological diseases, such as theagents identified above. In certain embodiments, conjointlyadministering one or more additional chemotherapeutic agents with acompound of the invention provides a synergistic effect. In certainembodiments, conjointly administering one or more additionalchemotherapeutics agents provides an additive effect.

The compound of the present invention can be used with one or more otherimmunomodulators and/or potentiating agents conjointly using a singlepharmaceutical composition or a combination of different pharmaceuticalcompositions. Suitable immunomodulators include various cytokines,vaccines and adjuvants. Examples of cytokines, vaccines and adjuvantsthat stimulate immune responses include GM-CSF, M-CSF, G-CSF,interferon-α, β or γ, IL-1, IL-2, IL-3, IL-12, Poly(I:C) and C_(p)G.

In certain embodiments, the potentiating agents includescyclophosphamide and analogs of cyclophosphamide, anti-TGFβ and Imatinib(Gleevec), a mitosis inhibitor, such as paclitaxel, Sunitinib (Sutent)or other antiangiogenic agents, an aromatase inhibitor, such asletrozole, an A2a adenosine receptor (A2AR) antagonist, an angiogenesisinhibitor, anthracyclines, oxaliplatin, doxorubicin, TLR4 antagonistsand IL-18 antagonists.

Definitions and Abbreviations

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning and the meaning of such terms is independent ateach occurrence thereof and is as commonly understood by one of skill inart to which the subject matter herein belongs. That notwithstanding andexcept where stated otherwise, the following definitions applythroughout the specification and claims. Chemical names, common names,and chemical structures may be used interchangeably to describe the samestructure. If a chemical compound is referred to using both a chemicalstructure and a chemical name and an ambiguity exists between thestructure and the name, the structure predominates. These definitionsapply regardless of whether a term is used by itself or in combinationwith other terms, unless otherwise indicated. Hence, the definition of“alkyl” applies to “alkyl” as well as the “alkyl” portions of“hydroxyalkyl,” “haloalkyl,” “—O-alkyl,” etc.

The term “compounds of the present invention” comprises compounds offormula (I), pharmaceutical acceptable salts thereof and stereoisomersthereof.

The term “acyl” is art-recognized and refers to a group represented bythe general formula hydrocarbylC(O)—, preferably alkylC(O)—.

The term “acylamino” refers to an amino group substituted with acyl.

The term “alkoxy” refers to an alkyl group, preferably a lower alkylgroup, having an oxygen attached thereto. Representative alkoxy groupsinclude methoxy, ethoxy, propoxy, tert-butoxy and the like.

The term “alkenyl”, as used herein, refers to an aliphatic groupcontaining at least one double bond and is intended to include both“unsubstituted alkenyls” and “substituted alkenyls”, the latter of whichrefers to alkenyl moieties having substituents replacing a hydrogen onone or more carbons of the alkenyl group. Such substituents may occur onone or more carbons that are included or not included in one or moredouble bonds. Moreover, such substituents include all those contemplatedfor alkyl groups, as discussed below, except where stability isprohibitive. For example, substitution of alkenyl groups by one or morealkyl, carbocyclyl, aryl, heterocyclyl or heteroaryl groups iscontemplated.

An “alkyl” group or “alkane” is a straight chained or branchednon-aromatic hydrocarbon which is completely saturated. Typically, astraight chained or branched alkyl group has from 1 to about 20 carbonatoms, preferably from 1 to about 10 unless otherwise defined. Examplesof straight chained and branched alkyl groups include methyl, ethyl,n-propyl, iso-propyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl,pentyl and octyl. A Cj-C straight chained or branched alkyl group isalso referred to as a “lower alkyl” group. An alkyl group may beoptionally substituted at one or more positions as permitted by valence.Such optional substituents include, for example, halogen, azide, alkyl,aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, alkoxyl, amino, nitro,sulfhydryl, imino, amido, phosphonate, phosphinate, carbonyl, carboxyl,silyl, ether, alkylthio, sulfonyl, sulfonamido, ketone, aldehyde, ester,heterocyclyl, aromatic or heteroaromatic moieties, —CF₃, —CN or thelike.

The term “alkylamino”, as used herein, refers to an amino groupsubstituted with at least one alkyl group.

The term “alkylthio”, as used herein, refers to a thiol groupsubstituted with an alkyl group and may be represented by the generalformula alkylS-.

The term “alkynyl”, as used herein, refers to an aliphatic groupcontaining at least one triple bond and is intended to include both“unsubstituted alkynyls” and “substituted alkynyls”, the latter of whichrefers to alkynyl moieties having substituents replacing a hydrogen onone or more carbons of the alkynyl group. Such substituents may occur onone or more carbons that are included or not included in one or moretriple bonds. Moreover, such substituents include all those contemplatedfor alkyl groups, as discussed above, except where stability isprohibitive. For example, substitution of alkynyl groups by one or morealkyl, carbocyclyl, aryl, heterocyclyl or heteroaryl groups iscontemplated.

The term “amide” or “amido” as used herein, refers to a group

wherein each R^(x) any R^(y) independently represent a hydrogen orhydrocarbyl group or both R^(x) any R^(y) are taken together with the Natom to which they are attached complete a heterocycle having from 4 to8 atoms in the ring structure.

The terms “amine” and “amino” are art-recognized and refer to bothunsubstituted and substituted amines and salts thereof, e.g., a moietythat can be represented by

wherein each R^(x) independently represents a hydrogen or a hydrocarbylgroup or two R^(x) are taken together with the N atom to which they areattached complete a heterocycle having from 4 to 8 atoms in the ringstructure.

The term “aminoalkyl”, as used herein, refers to an alkyl groupsubstituted with an amino group.

The term “aralkyl” or “arylalkyl”, as used herein, refers to an alkylgroup substituted with an aryl group.

The term “aryl” as used herein include substituted or unsubstitutedsingle-ring aromatic groups in which each atom of the ring is carbon.Preferably the ring is a 5- to 7-membered ring, more preferably a6-membered ring. The term “aryl” also includes polycyclic ring systemshaving two or more cyclic rings in which two or more carbons are commonto two adjoining rings wherein at least one of the rings is aromatic,e.g., the other cyclic rings can be cycloalkyls, cycloalkenyls,cycloalkynyls, aryls, heteroaryls and/or heterocyclyls. Aryl groupsinclude benzene, naphthalene, phenanthrene, phenol, aniline and thelike.

A “cycloalkyl” group is a cyclic hydrocarbon which is completelysaturated. “Cycloalkyl” includes monocyclic and bicyclic rings.Typically, a monocyclic cycloalkyl group has from 3 to about 10 carbonatoms, more typically 3 to 8 carbon atoms unless otherwise defined. Thesecond ring of a bicyclic cycloalkyl may be selected from saturated,unsaturated and aromatic rings. Cycloalkyl includes bicyclic moleculesin which one, two or three or more atoms are shared between the tworings. The term “fused cycloalkyl” refers to a bicyclic cycloalkyl inwhich each of the rings shares two adjacent atoms with the other ring.The second ring of a fused bicyclic cycloalkyl may be selected fromsaturated, unsaturated and aromatic rings. A “cycloalkenyl” group is acyclic hydrocarbon containing one or more double bonds. A cycloalkylgroup may be substituted at one or more positions, as permitted byvalence, with any optional substituents described herein. Cycloalkylgroups include but are not limited to cyclopropyl, cyclobutyl,cyclopentyl and cyclohexyl.

As used herein, the term “cyano” refers to —CN group.

The term “carboxy” or “carboxylic acid”, as used herein, refers to agroup represented by the formula —CO₂H.

The term “carboxylate” refers to a group represented by the formula—(CO₂)⁻.

The term “ester”, as used herein, refers to a group —C(O)OR^(x) whereinR^(x) represents a hydrocarbyl group.

As used herein, the term “guanidino” refers to —NH—C(═NH)—NH₂ group.

The terms “halo” and “halogen” as used herein means halogen and includeschloro, fluoro, bromo and iodo.

The term “haloalkyl”, as used herein, refers to an alkyl groupsubstituted with a halogen group.

As used herein, the term “carbocycle”, “carbocyclic” or “carbocyclyl” isintended to mean any stable 3-, 4-, 5-, 6- or 7-membered monocyclic orbicyclic or 7-, 8-, 9-, 10-, 11-, 12- or 13-membered bicyclic ortricyclic hydrocarbon ring, any of which may be saturated, partiallyunsaturated, unsaturated or aromatic. Examples of carbocycles include,but are not limited to, cyclopropyl, cyclobutyl, cyclobutenyl,cyclopentyl, cyclopentenyl, cyclohexyl, cycloheptenyl, cycloheptyl,cycloheptenyl, adamantyl, cyclooctyl, cyclooctenyl, cyclooctadienyl,[3.3.0]bicyclooctane, [4.3.0]bicyclononane, [4.4.0]bicyclodecane,[2.2.2]bicyclooctane, fluorenyl, phenyl, naphthyl, indanyl, adamantyl,anthracenyl and tetrahydronaphthyl (tetralin). As shown above, bridgedrings are also included in the definition of carbocycle (e.g.,[2.2.2]bicyclooctane). Preferred carbocycles, unless otherwisespecified, are cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, phenyland indanyl. When the term “carbocycle” or “carbocyclyl” is used, it isintended to include “aryl”. A bridged ring occurs when one or morecarbon atoms link two non-adjacent carbon atoms. Preferred bridges areone or two carbon atoms. It is noted that a bridge always converts amonocyclic ring into a tricyclic ring. When a ring is bridged, thesubstituents recited for the ring may also be present on the bridge.

The terms “hetaralkyl” and “heteroaralkyl”, as used herein, refers to analkyl group substituted with a hetaryl group.

The term “heteroalkyl”, as used herein, refers to a saturated orunsaturated chain of carbon atoms and at least one heteroatom, whereinno two heteroatoms are adjacent.

The terms “heteroaryl” and “hetaryl” include substituted orunsubstituted aromatic single ring structures, preferably 5- to7-membered rings, more preferably 5- to 6-membered rings, whose ringstructures include at least one heteroatom, preferably one to fourheteroatoms, more preferably one or two heteroatoms. The terms“heteroaryl” and “hetaryl” also include polycyclic ring systems havingtwo or more cyclic rings in which two or more carbons are common to twoadjoining rings wherein at least one of the rings is heteroaromatic,e.g., the other cyclic rings can be cycloalkyls, cycloalkenyls,cycloalkynyls, aryls, heteroaryls and/or heterocyclyls. Heteroarylgroups include, for example, pyrrole, furan, thiophene, imidazole,oxazole, thiazole, pyrazole, pyridine, pyrazine, pyridazine, indole,1,3,4-oxadiazole, pyrimidine and the like. A heteroaryl group may besubstituted at one or more positions, as permitted by valence, with anyoptional substituents described herein.

The term “heteroatom” as used herein means an atom of any element otherthan carbon or hydrogen. Preferred heteroatoms are nitrogen, oxygen andsulfur.

The terms “heterocyclyl”, “heterocycle” and “heterocyclic” refer tosubstituted or unsubstituted non-aromatic ring structures, preferably 3-to 10-membered rings, more preferably 3- to 7-membered rings, whose ringstructures include at least one heteroatom, preferably one to fourheteroatoms, more preferably one or two heteroatoms. The terms“heterocyclyl” and “heterocyclic” also include polycyclic ring systemshaving two or more cyclic rings in which two or more carbons are commonto two adjoining rings wherein at least one of the rings isheterocyclic, e.g., the other cyclic rings can be cycloalkyls,cycloalkenyls, cycloalkynyls, aryls, heteroaryls and/or heterocyclyls.Heterocyclyl groups include, for example, piperidine, piperazine,pyrrolidine, morpholine, 2,3-dihydrobenzo[b][1,4]dioxine, lactones,lactams and the like. Heterocyclyl groups may be optionally substitutedas permitted by valence.

The term “heterocyclylalkyl” or “(heterocyclyl)alkyl”, as used herein,refers to an alkyl group substituted with a heterocycle group.

The term “hydroxyalkyl”, as used herein, refers to an alkyl groupsubstituted with a hydroxy group.

As used herein, the term “hydroxy” or “hydroxyl” refers to —OH group.

As used herein, the term “nitro” refers to —NO₂ group.

The term “lower” when used in conjunction with a chemical moiety, suchas, acyl, acyloxy, alkyl, alkenyl, alkynyl or alkoxy is meant to includegroups where there are ten or fewer non-hydrogen atoms in thesubstituent, preferably six or fewer. A “lower alkyl”, for example,refers to an alkyl group that contains ten or fewer carbon atoms,preferably six or fewer. In certain embodiments, acyl, acyloxy, alkyl,alkenyl, alkynyl or alkoxy substituents defined herein are respectivelylower acyl, lower acyloxy, lower alkyl, lower alkenyl, lower alkynyl orlower alkoxy, whether they appear alone or in combination with othersubstituents, such as in the recitations hydroxyalkyl and aralkyl (inwhich case, for example, the atoms within the aryl group are not countedwhen counting the carbon atoms in the alkyl substituent).

The term “substituted” refers to moieties having substituents replacinga hydrogen on one or more carbons of the backbone. It will be understoodthat “substitution” or “substituted with” includes the implicit provisothat such substitution is in accordance with permitted valence of thesubstituted atom and the substituent and that the substitution resultsin a stable compound, e.g., which does not spontaneously undergotransformation such as by rearrangement, cyclization, elimination, etc.As used herein, the term “substituted” is contemplated to include allpermissible substituents of organic compounds. In a broad aspect, thepermissible substituents include acyclic and cyclic, branched andunbranched, carbocyclic and heterocyclic, aromatic and non-aromaticsubstituents of organic compounds. The permissible substituents can beone or more and the same or different for appropriate organic compounds.For purposes of this invention, the heteroatoms such as nitrogen mayhave hydrogen substituents and/or any permissible substituents oforganic compounds described herein which satisfy the valences of theheteroatoms. Substituents can include any substituents described herein,for example, a halogen, a hydroxyl, a carbonyl (such as a carboxyl, analkoxycarbonyl, a formyl or an acyl), a thiocarbonyl (such as athioester, a thioacetate or a thioformate), an alkoxyl, a phosphoryl, aphosphate, a phosphonate, a phosphinate, an amino, an amido, an amidine,an imine, a cyano, a nitro, an azido, a sulfhydryl, an alkylthio, asulfate, a sulfonate, a sulfamoyl, a sulfonamido, a sulfonyl, aheterocyclyl, an aralkyl or an aromatic or heteroaromatic moiety. Itwill be understood by those skilled in the art that substituents canthemselves be substituted, if appropriate. Unless specifically stated as“unsubstituted,” references to chemical moieties herein are understoodto include substituted variants. For example, reference to an “aryl”group or moiety implicitly includes both substituted and unsubstitutedvariants.

The term “thioalkyl”, as used herein, refers to an alkyl groupsubstituted with a thiol group.

The term “thioester”, as used herein, refers to a group —C(O)SR^(x) or—SC(O)R^(x) wherein R^(x) represents a hydrocarbyl.

The term “thioacid”, “thiocarboxy” or “thiocarboxylic acid”, as usedherein, refers to a group represented by the formula —C(O)SH.

The term “thiocarboxylate” refers to a group represented by the formula—(C(O)S)⁻.

As used herein, a therapeutic that “prevents” a disorder or conditionrefers to a compound that, in a statistical sample, reduces theoccurrence of the disorder or condition in the treated sample relativeto an untreated control sample or delays the onset or reduces theseverity of one or more symptoms of the disorder or condition relativeto the untreated control sample.

The term “treating” includes prophylactic and/or therapeutic treatments.The term “prophylactic or therapeutic” treatment is art-recognized andincludes administration to the host of one or more of the subjectcompositions. If it is administered prior to clinical manifestation ofthe unwanted condition (e.g., disease or other unwanted state of thehost animal) then the treatment is prophylactic (i.e., it protects thehost against developing the unwanted condition), whereas if it isadministered after manifestation of the unwanted condition, thetreatment is therapeutic, (i.e., it is intended to diminish, ameliorateor stabilize the existing unwanted condition or side effects thereof).

The term “prodrug” is intended to encompass compounds which, underphysiologic conditions, are converted into the therapeutically activeagents of the present invention (e.g., a compound of formula (I)). Acommon method for making a prodrug is to include one or more selectedmoieties which are hydrolyzed under physiologic conditions to reveal thedesired molecule. In other embodiments, the prodrug is converted by anenzymatic activity of the host animal. For example, esters or carbonates(e.g., esters or carbonates of alcohols or carboxylic acids) arepreferred prodrugs of the present invention. In certain embodiments,some or all of the compounds of formula (I) in a formulation representedabove can be replaced with the corresponding suitable prodrug, e.g.,wherein a hydroxyl in the parent compound is presented as an ester or acarbonate or carboxylic acid present in the parent compound is presentedas an ester.

As used herein, the term “comprise” or “comprising” is generally used inthe sense of include, that is to say permitting the presence of one ormore additional (unspecified) features or components.

As used herein, the term “including” as well as other forms, such as“include”, “includes,” and “included,” is not limiting.

As used herein, the term “amino acid” means a molecule containing bothan amino group and a carboxyl group and includes its salts, esters,combinations of its various salts, as well as tautomeric forms. Insolution, at neutral pH, amino and acid groups of an amino acid canexchange a proton to form a doubly ionized, through overall neutral,entity identified as a zwitterion. In some embodiments, the amino acidsare α-, β-, γ- or δ-amino acids, including their stereoisomers andracemates. As used herein, the term “L-amino acid” denotes an α-aminoacid having the levorotatory configuration around the α-carbon, that is,a carboxylic acid of general formula CH(COOH)(NH₂)-(side chain), havingthe L-configuration. The term “D-amino acid” similarly denotes acarboxylic acid of general formula CH(COOH)(NH₂)-(side chain), havingthe dextrorotatory-configuration around the α-carbon. Side chains ofL-amino acids can include naturally occurring and non-naturallyoccurring moieties. Non-naturally occurring (i.e., unnatural) amino acidside chains are moieties that are used in place of naturally occurringamino acid side chains in, for example, amino acid analogs.

An “amino acid residue” as used herein, means a moiety sharingstructural similarity to the parent amino acid. An amino acid residuemay be covalently bonded to another chemical moiety via the amino groupof the residue or the carboxylate group of the residue (i.e., a hydrogenatom of —NH₂ or —OH is replaced by a bond to another chemical moiety).

As used herein, the phrase “side chain of amino acid” means a moietythat is covalently attached to D or L-amino acid structure and can berepresented as CH(COOH)(NH₂)—R. For example, in case of alanineCH(COOH)(NH₂)(CH₃), side chain of amino acid (R) is —CH₃. Examples of“side chain of amino acid” include, but are not limited to,(C₁-C₆)alkyl, (C₂-C₆)alkenyl or (C₂-C₆)alkynyl. The side chain of aminoacid may be substituted by one or more, same or different substituentsselected from, but are not limited to, amino, amido, alkylamino,acylamino, carboxylic acid, carboxylate, thiocarboxylate, thioacid,-hydroxy, cycloalkyl, (cycloalkyl)alkyl, aryl, heterocyclyl, heteroaryl,guanidino, —SH, —S(alkyl); optionally wherein cycloalkyl, aryl,heterocyclyl and heteroaryl are further substituted by one or moresubstituents such as hydroxy, alkoxy, halo, amino, nitro, cyano oralkyl.

Amino acids include the twenty standard amino acids used by mostbiological organisms in protein synthesis. Unnatural amino acid residuesmay be selected from, but are not limited to, alpha andalpha-disubstituted amino acids, N-alkyl amino acids and natural aminoacids substituted with lower alkyl, aralkyl, hydroxyl, aryl, aryloxy,haloalkyl or acyl.

For example, lysine can be substituted to form an unnatural amino acid,e.g., at a carbon atom of its side chain or alternatively by mono- ordialkylation of its terminal NH₂ group (e.g., wherein the amino group ofthe lysine sidechain is taken together with its substituents to form aheterocyclic ring such as piperidine or pyrrolidine). In anotherexample, the terminal amino group of the lysine sidechain can form aring with the amino acid backbone, as in capreomycidine. Furtherunnatural derivatives of lysine include homolysine and norlysine. Thesidechain of lysine can alternatively be substituted by a second aminogroup. In another example, the alkyl portion of the lysine side chaincan be incorporated into a carbocyclic ring structure to form asemirigid analog, such as, e.g., cyclohexyl or cyclopentyl.

Throughout this specification and claims, the ‘L-threonine residue’and/or ‘side chain of L-threonine’ mentioned in compound of formula (I),and/or preparation thereof can be represented by any one of thefollowing formulae.

In certain embodiments, the unnatural amino acid can be a derivative ofa natural amino acid having one or more double bonds.

In other example embodiments, in threonine, the beta-methyl group can bereplaced with an ethyl, phenyl or other higher alkyl group. Inhistidine, the imidazole moiety can be substituted or alternatively, thealkylene backbone of the side chain can be substituted.

Further examples of unnatural amino acids include homoserine andhomologs of natural amino acids.

In further example embodiments, an unnatural amino acid can be alkylated(e.g., methylated) at the alpha position.

Further examples of unnatural amino acids include alpha, beta- and beta,gamma-dehydroamino amino acid analogs.

Further exemplary amino acids include penicillamine andbetamethoxyvaline.

Further examples of unnatural amino acids include the amino acidswherein the side chain comprises amino, alkylamino, acylamino,—COO-alkyl, cycloalkyl, heterocyclyl, heteroaryl, guanidino,(cycloalkyl)alkyl, (heterocyclyl)alkyl and (heteroaryl)alkyl.

“Modified N-terminal amino group” and “modified C-terminal carboxylgroup” mean that the amino group or carboxyl group is altered.

Modification of the N-terminal amino group is preferably with thegeneral formula —NR_(x)R_(y); wherein R_(x) is hydrogen or alkyl andR_(y) is alkyl, alkenyl, —C(═NH)NH₂, alkynyl, acyl, cycloalkyl, aryl orheterocyclyl.

Examples of N-terminal modifications include, but are not limited to,are acetylated, formylated or guanylated N-termini.

Modification of the C-terminal carboxyl group is preferably with thegeneral formula COR_(Z) (R_(z) replaces the hydroxyl group of the lastamino acid); wherein R_(z) is —NR₇R₈, alkoxy, amino or an imide. TheC-terminal carboxyl group may also be transformed into a heterocyclicring (such as a 1,2,4-oxadiaxole or 1,3,4-oxadiaxole ring) optionallysubstituted by hydroxy, alkyl, hydroxyalkyl, alkoxyalkyl or cycloalkyl.

This invention includes pharmaceutically acceptable salts of compoundsof the invention and their use in the compositions and methods of thepresent invention. In certain embodiments, contemplated salts of theinvention include, but are not limited to, alkyl, dialkyl, trialkyl ortetra-alkyl ammonium salts. In certain embodiments, contemplated saltsof the invention include, but are not limited to, L-arginine,benenthamine, benzathine, betaine, calcium hydroxide, choline, deanol,diethanolamine, diethylamine, 2-(diethylamino)ethanol, ethanolamine,ethylenediamine, N-methylglucamine, hydrabamine, 1H-imidazole, lithium,L-lysine, magnesium, 4-(2-hydroxyethyl)morpholine, piperazine,potassium, 1-(2-hydroxyethyl)pyrrolidine, sodium, triethanolamine,tromethamine and zinc salts. In certain embodiments, contemplated saltsof the invention include, but are not limited to, Na, Ca, K, Mg, Zn orother metal salts.

The pharmaceutically acceptable acid addition salts can also exist asvarious solvates, such as with water, methanol, ethanol,dimethylformamide and the like. Mixtures of such solvates can also beprepared. The source of such solvate can be from the solvent ofcrystallization, inherent in the solvent of preparation orcrystallization or adventitious to such solvent.

“Pharmaceutically acceptable” means that which is useful in preparing apharmaceutical composition that is generally safe, non-toxic and neitherbiologically nor otherwise undesirable and includes that which isacceptable for veterinary as well as human pharmaceutical use.

The term “stereoisomers” refers to any enantiomers, diastereoisomers orgeometrical isomers, such as of the compounds of the invention. Whencompounds of the invention are chiral, they can exist in racemic or inoptically active form. Since the pharmaceutical activity of theracemates or stereoisomers of the compounds according to the inventionmay differ, it may be desirable to use compounds that are enriched inone of the enantiomers. In these cases, the end product or even theintermediates can be separated into enantiomeric compounds by chemicalor physical measures known to the person skilled in the art or evenemployed as such in the synthesis. In the case of racemic amines,diastereomers are formed from the mixture by reaction with an opticallyactive resolving agent. Examples of suitable resolving agents areoptically active acids such as the R and S forms of tartaric acid,diacetyltartaric acid, dibenzoyltartaric acid, mandelic acid, malicacid, lactic acid, suitable N-protected amino acids (for exampleN-benzoylproline or N-benzenesulfonylproline) or the various opticallyactive camphorsulfonic acids. Also advantageous is chromatographicenantiomer resolution with the aid of an optically active resolvingagent (for example dinitrobenzoylphenylglycine, cellulose triacetate orother derivatives of carbohydrates or chirally derivatised methacrylatepolymers immobilised on silica gel).

In certain embodiments, compounds of the invention may be racemic. Incertain embodiments, compounds of the invention may be enriched in oneenantiomer. For example, a compound of the invention may have greaterthan 30% ee, 40% ee, 50% ee, 60% ee, 70% ee, 80% ee, 90% ee or even 95%or greater ee. In certain embodiments, compounds of the invention mayhave more than one stereocenter. In certain such embodiments, compoundsof the invention may be enriched in one or more diastereomer. Forexample, a compound of the invention may have greater than 30% de, 40%de, 50% de, 60% de, 70% de, 80% de, 90% de or even 95% or greater de.

The term “subject” includes mammals (especially humans) and otheranimals, such as domestic animals (e.g., household pets including catsand dogs) and non-domestic animals (such as wildlife).

Naturally-occurring amino acids are identified throughout thedescription and claims by the conventional three-letter abbreviationsindicated in the below table.

TABLE (Amino acid codes) Name 3-letter code Alanine Ala Arginine ArgAsparagine Asn Aspartic acid Asp Glutamic acid Glu Glutamine GlnHistidine His Isoleucine Ile Lysine Lys Methionine Met Phenylalanine PheProline Pro Serine Ser Threonine Thr Tyrosine Tyr Valine Val

The abbreviations used in the entire specification may be summarizedherein below with their particular meaning.

° C. (degree Celsius); % (percentage); brine (NaCl solution); CH₂Cl₂/DCM(Dichloromethane); Boc (Tert-butyloxycarbonyl); Bzl(Benzyloxy-carbonyl); Cs₂CO₃ (Caesium carbonate); DIC:N,N′-Diisopropylcarbodiimide; DIPEA (N,N-Diisopropylethylamine); DMF(Dimethyl formamide); EtOH (Ethanol); Et₂NH (Diethylamine); Fmoc(9-Fluorenylmethyloxycarbonyl); g or gr (gram); HOBt (1-Hydroxybenzotriazole); h or hr (Hours); HPLC (High-performance liquidchromatography); K₂CO₃ (Potassium carbonate); LCMS (Liquidchromatography mass spectroscopy); Liq.NH₃ (Liquid ammonia); mmol(Millimoles); M (Molar); μl (Microlitre); mL (Millilitre); mg(Milligram); MS (ES) (Mass spectroscopy-electro spray); min (Minutes);Na (Sodium); NaHCO₃ (Sodium bicarbonate); NH₂NH₂.H₂O (Hydrazinehydrate); NMM (N-Methylmorpholine); Na₂SO₄ (Sodium sulphate); NH₂OH.HCl(Hydroxylamine hydrochloride); PD1/PD-1 (Programmed cell death 1); PD-L1(Programmed death-ligand 1); PD-L2 (Programmed cell death 1 ligand 2);prep-HPLC/preparative HPLC (Preparative High-performance liquidchromatography); TEA/Et₃N (Triethylamine); TFAA: Tifluoroaceticanhydride; TLC (Thin Layer Chromatography); THF (Tetrahydrofuran); TIPS(Triisopropylsilane); TFA (Trifluoroacetic acid); t_(R) (Retentiontime); Trt (Trityl or Triphenylmethyl), etc.

EXPERIMENTAL

The present invention provides methods for the preparation of compoundsof formula (I) according to the procedures of the following examples,using appropriate materials. Those skilled in the art will understandthat known variations of the conditions and processes of the followingpreparative procedures can be used to prepare these compounds. Moreover,by utilizing the procedures described in detail, one of ordinary skillin the art can prepare additional compounds of the present invention.

The intermediates or starting materials required for the synthesis arecommercially available (commercial sources such as Sigma-Aldrich, USA orGermany; Chem-Impex USA; G.L. Biochem, China and Spectrochem, India) oralternatively, these intermediates or starting materials can be preparedusing known literature methods. The invention is described in greaterdetail by way of specific examples.

Purification and Characterization of Compounds Analytical HPLC Method:

Analytical HPLC was performed on ZIC HILIC 200 A° column (4.6 mm×250 mm,5 μm), Flow rate: 1.0 mL/min. The elution conditions used are: Buffer A:5 mmol ammonium acetate, Buffer B: Acetonitrile, Equilibration of thecolumn with 90% buffer B and elution by a gradient of 90% to 40% bufferB during 30 min.

Preparative HPLC Method:

Preparative HPLC was performed on SeQuant ZIC HILIC 200 A° column (10mm×250 mm, 5 μm), Flow rate: 5.0 mL/min. The elution conditions usedare: Buffer A: 5 mmol ammonium acetate (adjust to pH-4 with AceticAcid), Buffer B: Acetonitrile, Equilibration of the column with 90%buffer B and elution by a gradient of 90% to 40% buffer B during 20 min.

LCMS was performed on AP1 2000 LC/MS/MS triple quad (Applied biosystems)with Agilent 1100 series HPLC with G1315 B DAD, using Mercury MS columnor using Agilent LC/MSD VL single quad with Agilent 1100 series HPLCwith G1315 B DAD, using Mercury MS column or using Shimadzu LCMS 2020single quad with Prominence UFLC system with SPD-20 A DAD.

EXAMPLES Example 1: Synthesis of Compound 1 Step 1a

Ethylchloroformate (3.4 g, 31.3 mmol) and Et₃N (7.0 mL, 52.8 mmol) wereadded to a solution of compound 1a (5.0 g, 26.4 mmol) in THF (20 mL) andstirred at −20° C. for 20 min. After 20 minutes 25% of aqueous ammonia(10 mL, 132.0 mmol) was added to the active mixed anhydride and stirredat 0-5° C. for 30 min. The completeness of the reaction was confirmed byTLC analysis. The volatiles were evaporated under reduced pressure andpartitioned between water and ethyl acetate. The organic layer waswashed with NaHCO₃ solution followed by citric acid solution and brinesolution. The separated organic layer was dried over Na₂SO₄, filteredand evaporated under reduced pressure to yield 4.0 g of compound 1b.LCMS: 89.3 (M−Boc+H)⁺.

Step 1b

Trifluroacetic anhydride (8.4 g, 39.9 mmol) was added to a solution ofcompound 1b (5 g, 26.6 mmol) in pyridine (21.0 mL, 26.6 mmol) andstirred at room temperature for 2 h. The completeness of the reactionwas confirmed by TLC analysis. The volatiles were evaporated underreduced pressure and partitioned between water and ethyl acetate. Theorganic layer was washed with NaHCO₃ solution followed by citric acidsolution and brine solution. The separated organic layer was dried overNa₂SO₄, filtered and evaporated under reduced pressure to yield 3.5 g ofcompound 1c, which was used for next step directly.

Step 1c:

Hydroxylamine hydrochloride (0.92 g, 13.2 mmol), water (0.5 mL) andpotassium carbonate (1.8 g, 13.2 mmol) were added to a solution ofcompound 1c (1.5 g, 8.8 mmol) in EtOH (20 mL) and stirred at 86° C. for4 h. The completeness of the reaction was confirmed by TLC analysis. Thevolatiles were evaporated under reduced pressure and partitioned betweenwater and ethyl acetate. The organic layer was washed with brinesolution, dried over Na₂SO₄ then filtered and evaporated under reducedpressure to yield 0.9 g of compound 1d. LCMS: 104.3 (M−Boc+H)⁺.

Step 1d:

Deoxo-Fluor (3.7 g, 16.1 mmol) was added to a solution of Fmoc-Ala-OH(5.0 g, 15.0 mmol) in CH₂Cl₂ (50 mL) and stirred at 0° C. for 1 h. ThenCH₂Cl₂ was evaporated and triturated with hexane. Sodium acetate (0.2 g,2.4 mmol) and compound 1d (0.5 g, 2.4 mmol) in acetic acid were taken ina round neck flask and stirred for 30 minutes. To this mixture, wasadded Fmoc-Ala-COF (0.996 g, 3.1 mmol) and stirred at room temperaturefor 30 min. The reaction mixture was stirred at 90° C. for 3 h. Thecompleteness of the reaction was confirmed by TLC analysis. Thevolatiles were evaporated under reduced pressure and partitioned betweenwater and ethyl acetate. The organic layer was washed with NaHCO₃solution followed by citric acid solution and brine solution. Theseparated organic layer was dried over Na₂SO₄, filtered and evaporatedunder reduced pressure to get residue. The residue was purified bysilica gel column chromatography (eluent: 0-5% ethyl acetate in hexane)to yield 0.3 g of compound 1e. LCMS: 379.0 (M-Boc+H)⁺, 501.3 (M+Na)⁺.

Step 1e:

Diethylamine (1.0 mL) was added to a solution of compound 1e (0.35 g,0.73 mmol) in CH₂Cl₂ (10 mL). The mixture was stirred at roomtemperature for 3 h and then the resulting solution was concentratedunder nitrogen atmosphere and washed with diethyl ether and centrifugedto yield 0.18 g compound 1f, which was used for next step directly.

Step 1f:

The urea linkage was carried out using coupling of compound 1f (0.18 g,0.71 mmol) in DMF (5.0 mL) with compound 1h (0.24 g, 0.77 mmol) at roomtemperature. The coupling was initiated by the addition of TEA (0.2 mLg, 1.4 mmol) and the resultant mixture was stirred at room temperature.After the completion of 3 h, the reaction mass was partitioned betweenwater and ethyl acetate. The organic layer was washed with waterfollowed by brine solution and dried over Na₂SO₄. The separated organiclayer was filtered and evaporated under reduced pressure to yield 0.2 gof compound 1g. LCMS: 450.1 (M+Na)⁺.

Step 1g:

To a solution of compound 1g (0.15 g, 0.35 mmol) in CH₂Cl₂ (1 mL) wereadded trifluoroacetic acid (0.5 mL) and catalytic amount oftriisopropylsilane and stirred at room temperature for 3 h. Theresulting solution was concentrated under reduced pressure to yield 0.10g of crude compound. The crude solid material was purified as prep HPLCmethod described under experimental conditions. LCMS: 272.2 (M+H)⁺; HPLC(t_(R)): 6.2 min.

Synthesis of Compound 1h:

Pyridine (12.0 g, 25.2 mmol) was added to a solution of H-Ala-OtBu (2.3g, 12.6 mmol) in CH₂Cl₂ (20 mL) and the resulting solution was stirredat room temperature for 5-10 min. Solution of 4-Nitrophenylchloroformate (2.8 g, 13.8 mmol) in CH₂Cl₂ (20 mL) was added to theabove reaction mixture and stirring was continued at room temperaturefor 1 h. The completeness of the reaction was confirmed by TLC analysis.After completion of reaction it was diluted with CH₂Cl₂ (50 mL) andwashed with 1.0 M of sodium bisulphate solution (50 mL×2) followed by1.0 M sodium carbonate solution (50 mL×2). The organic layer was driedover Na₂SO₄, filtered and evaporated under reduced pressure to yieldcrude compound, which was purified by silica gel column chromatography(eluent: 0-20% ethyl acetate in hexane) to yield 2.0 g of compound 1h.

The below compounds were prepared by procedure similar to the onedescribed in Example 1 (compound 1) with appropriate variations inreactants or amino acids, solvents, quantities of reagents and reactionconditions. The analytical data of the compounds are summarized hereinbelow table.

Compound LCMS HPLC No. Structure (M + H)⁺ (t_(R) in min) 2.

403.2 12.6 3.

373.1 9.4 4.

389.1 13.1 5.

388.1 21.9 6.

344.2 12.4

Example 2: Synthesis of Compound 7

Step-2a:

Compound 2a was synthesized using similar procedure as depicted in step1a to 1c of Example 1 (Compound 1) by using Boc-Tyr(tBu)-OH instead ofBoc-Ala-OH to yield 9 g compound 2a.

Step-2b:

HOBt (3.45 g, 30.8 mmol) and DIC (4.5 mL, 30.8 mmol) were added to asolution of Fmoc-Pro-OH (8.6 g, 25.6 mmol) in DMF (250 mL) at 0° C. andstirred for 30 minutes. Compound 2a (9 g, 25.6 mmol) was further addedto the above reaction mixture at the same temperature and continuedstirring for 2 h at 0° C. followed by 2 h at room temperature. Thecompleteness of the reaction was confirmed by TLC analysis. The reactionmixture was quenched with ice water, the precipitated white solid wasfiltered, washed with water (1 L) and dried under high under reducedpressure. The solid was stirred with diethyl ether (500 mL) for 15 min,filtered and dried to yield 14 g of compound 2b. LCMS: 671.3 (M+H)⁺,693.3 (M+Na)⁺.

Step 2c:

To a solution of compound 2b (13 g, 19.4 mmol) in acetonitrile (130 ml),was added acetic acid (10.0 mL) at room temperature and refluxed at 85°C. for 12 h. The completeness of the reaction was confirmed by TLCanalysis. The volatiles were evaporated under reduced pressure to obtaincrude semi solid which was diluted with water and ethyl acetate. Theorganic layer was washed with NaHCO₃ solution followed by citric acidsolution and brine solution. The organic layer was dried over Na₂SO₄,filtered and evaporated under reduced pressure to yield crude solidwhich was diluted with 10% acetonitrile in hexane (500 ml) and stirredfor 2 h to obtain white solid. The white solid was filtered and washedwith n-pentane (500 L) and dried to yield 13 g of compound 2c. LCMS:653.4 (M+H)⁺, 675.6 (M+Na)⁺.

Step 2d:

Compound 2c (13 g, 19.9 mmol) was added to a solution of 20% piperidinein DCM (150 mL) at 0° C. and stirred at 0° C. for 1 h. The completenessof the reaction was confirmed by TLC analysis. The reaction mixture wasconcentrated under reduced pressure and diluted with hexane, stirred andfiltered. The filtered solid was dissolved in EtOAc and washed with sat.NaHCO₃ solution, brine solution, dried over Na₂SO₄ filtered andevaporated to yield white compound 2d. LCMS 431.1 (M+H)⁺; 453.4 (M+Na)⁺.

Step 2e:

DIPEA was added to a solution of compound 2e (5 g, 11.6 mmol) andcompound 2d (5.3 g, 11.6 mmol) in dry THF (50 mL) at 0° C. and stirredfor 2 h. The reaction mixture was allowed to stir at ambient temperaturefor an additional 4 h. The volatiles were evaporated and portionedbetween ethyl acetate and water. The organic layer was washed withsaturated NaHCO₃ 10% citric acid, brine solution, dried over Na₂SO₄ andconcentrated under reduced pressure. The crude compound was purified bycolumn chromatography over neutral alumina using 25% ethyl acetate inhexane to yield compound 2f. LCMS: 772.5 (M+Na)⁺.

Step 2f:

A solution of compound 2f (6.5 g, 8.7 mmol) and trifluoroacetic acid (16mL) in DCM (16 mL) were stirred at 0° C. for one hour. The resultingreaction mixture was evaporated under reduced pressure, diluted withdiethyl ether and filtered to yield 4 g of crude compound. The crudesolid material was purified by preparative HPLC method described underexperimental conditions. LCMS: 482.3 (M+H)⁺; HPLC: t_(R)=12.92 min.

Synthesis of Compound 2e:

The compound was synthesized using similar procedure as depicted forcompound 1h in Example 1, by using H-Tyr(tBu)-OtBu instead ofH-Ala-OtBu.

The below compounds were prepared by procedure similar to the onedescribed in Example 2 (Compound 7) with appropriate variations inreactants or amino acids, solvents, quantities of reagents and reactionconditions. The analytical data of the compounds are summarized hereinbelow table.

Compound LCMS HPLC No. Structure (M + H)⁺ (t_(R), min) 8.

402.3 11.87 9.

387.0 11.8 10.

428.9 9.2 11.

375.1 10.6 12.

443.2 — 13.

421 11.0 14.

394.3 7.6 15.

345.3 12.7 16.

360.3 8.4 17.

318.0 11.3 18.

331.0 12.5 19.

498.4 7.6 20.

496.3 5.6 21.

420.3 7.7 22.

450.4 11.4 23.

386.1 14.5 24.

400.0 14.0 25.

325.7 10.3 26.

499.3 9.4 27.

417.3 13.1 28.

387.9 14.9 29.

401.3 14.0 30.

416.2 13.4 31.

388.1 11.2 32.

431.2 18.9 33.

444.4 12.2 34.

412.2 15.4 35.

439.3 11.5 36.

402.4 11.9 37.

403.1 8.5 38.

417.0 8.4 39.

407.5 12.2 40.

373.1 12.7 41.

460.2 11.9 42.

437.2 12.9 43.

433.3 11.6 44.

346.5 11.9 45.

400.1 10.6 46.

419.0 12.7 47.

320.1 14.9 48.

404.1 14.7 49.

385.1 12.6 50.

427.0 10.9 51.

493.3 13.8 52.

386.1 8.5 53.

495.0 11.2 54.

359.0 14.0 56.

401.0 13.6 58.

374.9 14.1 59.

416.1 12.9 60.

420.1 10.6 62.

403.9 9.2 63.

403.1 14.8 64.

458.5 11.8 65.

814.1 14.9 73.

391.6 — 74.

386.1 —

Example 3: Synthesis of Compound 75

The compound was synthesized using similar procedure as depicted inExample 2 by using compound 3b (prepared as per the procedure givenbelow) instead of Fmoc-Pro-OH. The crude solid material was purifiedusing preparative HPLC described under experimental conditions. LCMS:417.5 (M+H)⁺, HPLC: t_(R)=12.2 min.

Synthesis of Compound 3b: Step 3a:

Propylamine (2.9 mL, 35.25 mmol), HATU (14.8 g, 38.8 mmol) and DIPEA(12.3 mL, 70.5 mmol) were added to a solution of Fmoc-Glu-OtBu (15.0 g,35.3 mmol) in DMF (50 mL) at 0° C. and stirred at room temperature for1.5 h. The completion of the reaction was confirmed by TLC analysis. Thereaction mixture was quenched with water, the resulting solid wasfiltered, washed with diethyl ether, dried under reduced pressure toyield compound 3a (19.0 g) and used for the next step withoutpurification. LCMS: 489.4 (M+Na+H)⁺.

Step 3b:

To a solution of compound 3a (19.0 g, 40.72 mmol) in trifluoroaceticacid (19.0 mL) catalytic amount of triisopropylsilane was added andstirred at room temperature for 4 h. The resulting solution wasevaporated under nitrogen, washed with diethyl ether to obtain 13.3 g ofcrude compound which was used for the next step without purification.LCMS: 417.5 (M+H)⁺.

The below compounds were prepared by procedure similar to the onedescribed in Example 3 with appropriate variations in reactants or aminoacids, solvents, quantities of reagents and reaction conditions. Theanalytical data of the compounds are summarized herein below table.

Compound LCMS HPLC No. Structure (M + H)⁺ (t_(R), min) 76.

459.3  9.8 77.

445.0  9.6 78.

587.3 10.7

Example 4: Synthesis of Compound 79

The compound was synthesized using similar procedure as depicted inExample 2 by using compound 4f (as per the procedure given below)instead of H-Tyr(tBu)-OtBu. The crude solid material was purified usingpreparative HPLC described under experimental conditions. LCMS: 415.0(M+H)⁺, HPLC: t_(R)=13.1 min.

Synthesis of Compound 4f: Step 4a:

Methyl Iodide (4.9 g, 34 mmol) and potassium carbonate (6.0 g, 44 mmol)were added to the solution of compound 4a (7.1 g, 22 mmol) in DMF (70mL) and stirred at room temperature for 3 h. The completeness of thereaction was confirmed by TLC analysis. The reaction mixture waspartitioned between ice water and ethyl acetate. Organic layer waswashed with brine solution, dried over Na₂SO₄ and evaporated underreduced pressure to yield 6.4 g of compound 4b. LCMS: 324.0 (M+H)⁺.

Step 4b:

Hydrazine hydrate (6.4 mL) was added to the solution of compound 4b (6.4g) in methanol (64 mL) and stirred at room temperature for 12 h. Thecompleteness of the reaction was confirmed by TLC analysis. The reactionmixture was partitioned between ice water and ethyl acetate. Organiclayer was washed with brine solution, dried over Na₂SO₄ and evaporatedunder reduced pressure to yield 5.5 g of compound 4c. LCMS: 324.2(M+H)⁺].

Step 4c:

2-(tert-butoxy)acetic acid (1.16 g, 8.8 mmol), HOBT (1.3 g, 9.6 mmol),EDC.HCl (1.83 g, 9.6 mmol), DIPEA (2.5 g, 21 mmol) were added to thesolution of compound 4c (2.6 g, 8.8 mmol) in DMF (50 mL) and stirred atroom temperature for 4 h. The completeness of the reaction was confirmedby TLC analysis. The reaction mixture was partitioned between ice waterand ethyl acetate. Organic layer was washed with NaHCO₃, Citric acidbrine solution, dried over Na₂SO₄ and evaporated under reduced pressureto yield crude compound 6, which was further purified by silica gelcolumn chromatography (eluent: 0-50% ethyl acetate in Hexane) to yield 3g of product 4d. LCMS: 438.2 (M+H)⁺.

Step 4d:

Triphenyl phosphine (6.5 g, 24 mmol), Iodine (6.2 g, 24 mmol), TEA (3.5g, 35 mmol) were added to the solution of compound 4d (3.1 g, 7.0 mmol)in THF (50 mL) and DMF (10 mL) and stirred at room temperature for 3 h.The completeness of the reaction was confirmed by TLC analysis. Thereaction mixture was partitioned between sodium thiosulfate solution andethyl acetate. Organic layer was washed with brine solution, dried overNa₂SO₄ and evaporated under reduced pressure to yield crude compound 4e,which was further purified by silica gel column chromatography (eluent:0-50% ethyl acetate in Hexane) to yield 2.4 g of product 4e. LCMS: 420.2(M+H)⁺.

Step 4e:

Palladium hydroxide (0.5 g) was added to the solution of compound 4e(2.3 g) in methanol (30 mL) and stirred under H₂ gas at room temperaturefor 2 h. The completeness of the reaction was confirmed by TLC analysis.The reaction mixture was filtered on celite bed and the filtrateevaporated under reduced pressure to yield 1.2 g of product 4f. LCMS:286.1 (M+H)*.

Step 4f:

4-Nitro phenyl chloroformate (0.85 g, 4.2 mmol), Pyridine (0.36 g, 4.6mmol) were added to the solution of compound 4f (1.2 g, 4.2 mmol) inCH₂CL₂ (40 mL) and stirred at room temperature for 1 h. The completenessof the reaction was confirmed by TLC analysis. The reaction mixture waspartitioned between ice water and ethyl acetate. Organic layer waswashed with Citric acid brine solution, dried over Na₂SO₄ and evaporatedunder reduced pressure to yield crude compound 4g, which was furtherpurified by silica gel column chromatography (eluent: 0-40% ethylacetate in Hexane) to yield 1.8 g of product 4g.

Example 5: Synthesis of Compound 80

This compound was synthesized using similar procedure as depicted inExample 2 by using compound 5b (prepared as per the procedure givenbelow) instead of H-Tyr(tBu)-OtBu. The crude solid material was purifiedusing preparative HPLC described under experimental conditions. LCMS:431.5 (M+H)⁺, HPLC: t_(R)=12.6 min.

Synthesis of Compound 5b: Step 5a:

To a solution of Fmoc-Thr(tBu)-OH (5.5 g, 13.8 mmol) in DMF (25.0 mL)K₂CO₃ (2.9 g, 20.8 mmol) was added at 0° C. and stirred for 30 minutesfollowed by addition of iodopentane (2.1 mL, 16.6 mmol) at 0° C. Theabove reaction mixture was stirred at room temperature for 14 h. Thecompletion of the reaction was confirmed by TLC analysis. The reactionmixture was partitioned between water and ethyl acetate. Organic layerwas washed with NaHCO₃, brine solution, dried over Na₂SO₄ and evaporatedunder reduced pressure to yield compound 5a (6.86 g) and used for thenext step without purification.

LCMS: 246.4 (M−Fmoc+H)⁺.

Step 5b:

To compound 5a (6.86 g, 14.67 mmol) 20% of piperidine in CH₂Cl₂ (34.3mL) was added and the reaction mixture was stirred at room temperaturefor 1 h. The completeness of the reaction was confirmed by TLC analysis.The reaction mixture was evaporated under nitrogen and partitionedbetween water and ethyl acetate. Organic layer was washed with NaHCO₃,brine solution, dried over Na₂SO₄ and evaporated under reduced pressure.The crude compound 5b was purified by silica gel column chromatography(Eluent: 0-40% ethyl acetate in hexane to get 2.5 g of 5b. LCMS: 246.1(M+H)⁺.

Example 6: Synthesis of Compound 81

The compound was synthesized using similar procedure as depicted inExample 2 by using compound 6b (prepared as per the procedure givenbelow) instead of H-Tyr(tBu)-OtBu. The crude solid material was purifiedusing preparative HPLC described under experimental conditions. LCMS:443.8 (M+H)⁺, HPLC: t_(R)=8.8 min.

Synthesis of compound 6b:

Step 6a:

To a solution of Fmoc-Gln(Trt)-OH (5.0 g, 8.2 mmol) in DMF (25.0 mL)HATU (3.4 g, 9.0 mmol), H-Thr(OtBu)-OtBu (1.9 g, 8.2 mmol) and DIPEA(2.9 mL, 16.4 mmol) were added at 0° C. and stirred at room temperaturefor 2 h. The completion of the reaction was confirmed by TLC analysis.The reaction mixture was quenched with water, the resulting solid wasfiltered, washed with hexane and dried to yield 7.4 g of compound 6a.LCMS: 824.1 (M+H)⁺.

Step 6b

To compound 6a (7.4 g, 8.9 mmol) 20% of piperidine in CH₂Cl₂ (37.0 mL)was added, the reaction mixture was stirred at room temperature for 2 h.The completeness of the reaction was confirmed by TLC analysis. Thereaction mixture was evaporated under nitrogen and partitioned betweenwater and DCM. Organic layer was washed with NaHCO₃, brine solution,dried over Na₂SO₄ and evaporated under reduced pressure. The crudecompound was washed with hexane and dried under reduced pressure toyield 3.7 g of compound 6b. LCMS: 601.8 (M+H)⁺.

Example 7: Synthesis of Compound 82

The compound was synthesized using similar procedure as depicted inExample 2 by using compound 7c (prepared as per the procedure givenbelow) instead of compound 2d. The crude solid material was purifiedusing preparative HPLC described under experimental conditions. LCMS:443.8 (M+H)⁺, HPLC: t_(R)=8.8 min.

Synthesis of Compound 7c: Step 7a:

EDC.HCl (2.9 g, 14.97 mmol), HOBt (2.3 g, 14.97 mmol), Fmoc-Gly-OH (2.97g, 9.98 mmol) and NMM (2.7 mL, 24.95 mmol) were added to a solution ofcompound 7a (5.83 g, 9.98 mmol, The compound 7a was synthesized usingsimilar procedure as depicted for compound 2d in example-2) in DMF (30.0mL) at 0° C. and stirred room temperature for 18 h. The reaction mixturewas partitioned between water and ethyl acetate. Organic layer waswashed with citric acid, NaHCO₃, brine solution, dried over Na₂SO₄ andevaporated under reduced pressure, which was further purified by silicagel column chromatography (Eluent: 10% ethyl acetate in hexane-100%ethyl acetate) to yield 6.0 g of compound 7b. LCMS: 885.4 (M+Na+H)⁺.

Step 7b:

Diethyl amine (24.0 mL) was added to the solution of compound 7b (6.0 g,6.95 mmol) in CH₂Cl₂ (24.0 mL). The reaction was stirred for 6 h at roomtemperature and the resulting solution was concentrated under nitrogenatmosphere to yield compound 7c which was purified by silica gel columnchromatography (Eluent: 0-10% ethyl acetate in hexane then 2% methanolin DCM) to yield 4.5 g of compound 7c. LCMS: 641.2 (M+H)⁺.

Example 8: Synthesis of Compound 83

Step 8a:

Ethylchloroformate (2.35 mL, 25.05 mmol) and N-Methylmorpholine (2.75mL, 25.05 mmol) were added to a solution of compound 8a (5.0 g, 8.35mmol) in THF (50 mL) and stirred at −20° C. After 20 min. aqueousammonia (3.0 mL) was added to the active mixed anhydride formed in-situand stirred at 0-5° C. for 1 h. The completeness of the reaction wasconfirmed by TLC analysis. The reaction mixture was poured into waterand hexane, the resulting solid was filtered, washed with hexane anddried to get 4.2 g of compound 8b. LCMS: 596.3 (M+H)⁺.

Step 8b:

Triethyl amine (3.5 mL, 24.7 mmol) and Trifluroacetic anhydride (1.5 mL,10.6 mmol) were added to a solution of compound 8b (4.2 g, 7.1 mmol) inTHF (70 mL) and stirred at 0° C. for 1 h. The completeness of thereaction was confirmed by TLC analysis. The reaction mixture waspartitioned between water and ethyl acetate. Organic layer was washedwith NaHCO₃, brine solution, dried over Na₂SO₄ and evaporated underreduced pressure to yield 4 g of crude compound 8c which was used forthe next step without further purification. LCMS: 578.2 (M+H)⁺, 600.2(M+Na)⁺.

Step 8c:

To compound 8c (1.5 g, 2.59 mmol) 20% of piperidine in CH₂Cl₂ (20.0 mL)was added and the reaction mixture was stirred at 0° C. for 1 h. Thecompleteness of the reaction was confirmed by TLC analysis. The reactionmixture was evaporated under nitrogen and partitioned between water andethyl acetate. Organic layer was washed with NaHCO₃, brine solution,dried over Na₂SO₄ and evaporated under reduced pressure. The crudecompound was washed with hexane and 20% diethyl ether in hexane to yield0.8 g of compound 8d which was used for the next step without furtherpurification. LCMS: 378.4 (M+Na)⁺.

Step 8d:

Triethyl amine was added to a solution of compound 8d (0.8 g, 2.3 mmol)in DMF (15.0 mL) at 0° C. over a period of 2 minute. This was followedby the addition of compound 8i (1.0 g, 27.0 mmol). The reaction mixturewas stirred at room temperature for 2 h. The completeness of thereaction was confirmed by TLC analysis. The reaction mixture was pouredinto water and the resulting solid was filtered, washed with hexane and20% diethyl ether in hexane to yield 1.2 g of compound 8e. LCMS 613.6(M+H)⁺.

Step 8e:

Hydroxylamine hydrochloride (0.204 g, 29.37 mmol), water (10.0 mL) andpotassium carbonate (0.4 g, 29.37 mmol) were added to a solution ofcompound 8e (1.2 g, 19.58 mmol) in EtOH (26.0 mL) and stirred at 85° C.for 2 h. The completeness of the reaction was confirmed by TLC analysis.The reaction mixture was evaporated under reduced pressure and quenchedwith water, the resulting solid was filtered, washed with hexane anddried to yield 1.0 g of compound 8f. LCMS: 646.9 (M+H)⁺.

Step 8f:

DIC (0.29 mL, 18.58 mmol) and HOBt (0.25 g, 18.58 mmol) were added to asolution of Boc-Ser(tBu)-OH (0.4 g, 15.48 mmol) in DMF (20.0 mL) at 0°C. and stirred for 30 minutes followed by addition of compound 8f (1.0g, 15.48 mmol) and stirred at room temperature for 1.5h. Thecompleteness of the reaction was confirmed by TLC analysis. The reactionmixture was quenched with water, the resulting solid was filtered,washed with diethyl ether, dried under reduced pressure to get 1.4 g ofcompound 8g, which used for the next step without further purification.LCMS: 889.4 (M+H)⁺.

Step 8g:

Acetic acid (1.2 mL) was added to a solution of compound 8g (1.2 g,13.49 mmol) in 2-methyl THF (30.0 mL). The reaction mixture was stirredat 84° C. for 12 h. The completeness of the reaction was confirmed byTLC analysis. The reaction mixture was partitioned between water andethyl acetate. Organic layer was washed with NaHCO₃, brine solution,dried over Na₂SO₄ and evaporated under reduced pressure. The crudecompound was washed with hexane and 5% diethyl ether in hexane to get0.45 g of compound 8h which was used for the next step without furtherpurification. LCMS: 871.4 (M+H)⁺.

Step 8h:

To a solution of compound 8h (0.4 g, 4.55 mmol) in trifluoroacetic acid(9.5 mL), triisopropylsilane (0.25 mL) and water (0.25 mL) were addedand stirred at room temperature for 2 h. The resulting solution wasevaporated under nitrogen to obtain 0.1 g of crude compound 83. Thecrude solid material was purified using preparative-HPLC methoddescribed under experimental conditions. LCMS: 361.1 (M+H)⁺; HPLC:t_(R)=13.9 min.

Synthesis of Compound 8i:

To a solution of HCl.H-Thr(^(t)Bu)-O^(t)Bu (8 g, 29.9 mmol) in CH₂Cl₂(80 mL), was added pyridine (5.9 g, 74.0 mmol) and the solution wasstirred for 5-10 min at room temperature. To this, a solution of4-nitrophenyl chloroformate (7.2 g, 35.0 mmol) in CH₂Cl₂ was added andthe resultant mixture was stirred for 30 min at room temperature. Thecompletion of the reaction was confirmed by TLC analysis. Aftercompletion of reaction, the reaction mixture was diluted with CH₂Cl₂ andwashed with water and 5.0 M citric acid solution. The separated organiclayer was dried over Na₂SO₄, filtered and evaporated under reducedpressure to get crude compound, which was purified by silica gel columnchromatography (eluent: 0-20% ethyl acetate in hexane) to yield 9 g ofcompound 8i. LCMS: 397.3 (M+H)⁺.

Example 9: Synthesis of Compound 84

Step 9a:

To a stirred solution of compound 9a (1.00 g) in DCM (40.0 mL) was addedpyridine (0.33 mL) followed by cyclopropane sulfonyl chloride (0.33 mL)and the resultant mixture was stirred at ambient conditions for 16 h,when TLC-analysis has indicated the completion of the reaction. Thereaction mixture was partitioned between water and DCM and the organiclayer was washed with dil. HCl (1.0 N). The organic phase was then driedover Na₂SO₄ and was concentrated under reduced pressure to furnish thecrude sulphonamide, which was further purified by column chromatography(neutral alumina, eluent Hexane-EtOAc (2:3)) to furnish the desiredCompound 9b (1.10 g). LCMS: 735.4 (M+H+H₂O)⁺.

Step 9b:

The compound 84 was prepared from compound 9b according to the proceduredescribed in step 1g of Example—1 with appropriate variations inreactants, quantities of reagents, solvents and reaction conditions.LCMS (M+H)⁺: 319.9

The below compounds were prepared by procedure similar to the onedescribed in Example 9 (Compound 84) with appropriate variations inreactants or amino acids, solvents, quantities of reagents and reactionconditions. The analytical data of the compounds are summarized hereinbelow table.

Compound LCMS No. Structure (M + H)⁺ 85.

336.2 86.

308.3 87.

322.3 88.

348.2 89.

362.3 90.

413.1

Example 10: Synthesis of Compound 91

Step 10a:

DIPEA (0.11 g, 0.89 mmol) was added under inert atmosphere to a stirredsolution containing compound 10a (0.25 g, 0.4 mmol), carboxylic acid 10c(74 mg, 0.44 mmol) and HATU (0.23 g, 0.61 mmol) in dry DMF (3.0 mL). Thereaction mixture was stirred at ambient conditions for 16 hand Theresultant reaction mixture was partitioned between water (50 mL) andEtOAc (25 mL) and the aqueous layer was extracted with EtOAc (25 mL×3).Combined organic phases were washed once with cold water, dried overNa₂SO₄ and the solvent was removed under reduced pressure to furnish thecompound 10b (0.12 g). LCMS: 779.0 (M+H+H₂O)⁺.

Step 10b:

The compound 90 was prepared from compound 10b according to theprocedure described in step 1g of Example—1 with appropriate variationsin reactants, quantities of reagents, solvents and reaction conditions.LCMS (M+H)⁺: 363.9

The below compounds were prepared by procedure similar to the onedescribed in Example 10 (Compound 91) with appropriate variations inreactants or amino acids, solvents, quantities of reagents and reactionconditions. The analytical data of the compounds are summarized hereinbelow table.

Compound LCMS No. Structure (M + H)⁺ 92.

329.3 93.

317.1

Example 11: Synthesis of Compound 94

Step 11a:

To a stirred solution of 11a (2.00 g) in DCM (40.0 mL) was addedpyridine (0.53 mL) followed by 4-nitrophenyl chloroformate (0.65 g) andthe resultant mixture was stirred at ambient conditions for 16 h.. Thereaction mixture was further partitioned between water and DCM and theorganic layer was washed with dil. HCl (1.0 N). The organic phase wasthen dried over Na₂SO₄ and was concentrated under reduced pressure tofurnish the crude sulphonamide, which was further purified by columnchromatography (neutral alumina, eluent Hexane-EtOAc (2:3)) to furnishthe desired carbamate 11b (2.66 g). LCMS: 801.4 (M+H+Na)⁺.

Step 11b:

Amine 11e (0.55 g, 4.09 mmol) was added to a stirred solution ofcompound 11b (2.66 g, 3.41 mmol) in Ethanol (30.0 mL) and the resultantmixture was refluxed at 75° C. for 16 h. The completeness of thereaction was confirmed by TLC analysis. The reaction mixture wasevaporated under reduced pressure, diluted with ethyl acetate (75 mL)and was sequentially washed with water (80 mL) followed by sat. K₂CO₃solution (50 mL) and brine (50 mL). After drying the organics overNa₂SO₄, solvents were removed under reduced pressure to furnish thecompound 11c (1.0 g). LCMS: 775.3 (M+H)⁺.

Step 11c:

The compound 91 was prepared from compound 11c according to theprocedure described in step 1g of Example—1 with appropriate variationsin reactants, quantities of reagents, solvents and reaction conditions.LCMS (M+H)⁺: 377.2

Example 12: Synthesis of Compound 95

Step 12a:

Acetic acid (0.2 mL) was added to a stirred solution of compound 12a(500 mg) and compound 12d (134 mg) in dry DCE (20.0 mL) and theresultant mixture was stirred at RT for 12 h. Sodium borohydride (77.0mg) was added to the above mixture and the resultant mixture was stirredat ambient temperature for 4 h.. The reaction mixture was diluted withwater (25 mL) and was extracted with DCM (3×25 mL). Combined organicphases were washed with brine and water, dried over Na₂SO₄ and thesolvents were removed under reduced pressure to furnish the crudecompound 12b, which was carried forward to the next step without furtherpurification (200 mg). LCMS: 708.0 (M+H)⁺.

Step 12b:

The compound 92 was prepared from 12b according to the proceduredescribed in step 1g of Example—1 with appropriate variations inreactants, quantities of reagents, solvents and reaction conditions.LCMS (M+H)⁺: 310.2

Example 13: Synthesis of Compound 96

Step 13a:

Compound 13d (77.0 mg) was added to a stirred solution of compound 13a(0.3 g) in Toluene (10.0 mL) under inert atmosphere and the resultantmixture was heated at 60° C. for 16 h. The solvent was removed underreduced pressure, the crude product was repeatedly washed with pentane(2×10 mL) and diethyl ether (2×10 mL) and was dried under reducedpressure to furnish compound 13b (200.0 mg). LCMS: 702.0 (M+H−^(t)Bu)⁺.

Step 2:

The compound 96 was prepared from 13b according to the proceduredescribed in step 1g of Example—1 with appropriate variations inreactants, quantities of reagents, solvents and reaction conditions.LCMS (M+H)⁺: 360.0

Example 14: Synthesis of Compound 97

Step 14a:

A solution of 4-nitrophenol (1.3 g, 9.99 mmol) and pyridine (0.8 mL,9.99 mmol) in Et₂O (20 mL) were added dropwise to a solution of SO₂Cl₂(0.8 mL, 9.99 mmol) in Et₂O (20 mL) at −78° C. under argon. The reactionmixture allowed to warm to room temperature, stirred for 4 h. Thecompleteness of the reaction was confirmed by TLC analysis. Thevolatiles were evaporated under reduced pressure to yield crudecompound. The crude compound was purified by silica gel columnchromatography (Eluent: 0-3% ethyl acetate in hexane) and resulted in1.2 g of compound 14a. ¹H NMR (400 MHz, CDCl₃): δ 8.39-8.36 (m, 2H),7.61-7.57 (m, 2H).

Step 14b:

A mixture of compound 14b (0.6 g, 2.59 mmol), molecular sieves (1.0 g),4-nitrophenol (0.72 g, 5.18 mmol) and Et₃N (1.1 mL, 7.77 mmol) in dryCH₂Cl₂ (25.0 mL), were added dropwise to a solution of compound 14a (1.2g, 5.18 mmol) in dry CH₂Cl₂ (5.0 mL) at−78° C. under argon atmosphere.After stirring for 30 minutes. the reaction mixture allowed to warm toroom temperature for 2 h. The completeness of the reaction was confirmedby TLC analysis. The reaction mixture was evaporated under reducedpressure to yield crude compound. The crude compound was purified bysilica gel column chromatography (Eluent: 0-7% ethyl acetate in hexane)and resulted in 0.7 g of compound 14c. ¹H NMR (300 MHz, CDCl₃): δ8.30-8.27 (m 2H), 7.52-7.49 (m 2H), 5.70-5.67 (1H d, J 9.6), 4.17-3.90(1H, m), 1.49 (9H, s), 1.28-1.23 (3H, m), 1.15 (9H, s).

Step 14c:

Compound 14c (0.69 g, 1.59 mmol) in THF (5.0 mL) was added to a stirredsolution of compound 14d (0.7 g, 1.14 mmol) and Et₃N (0.5 mL, 3.42 mmol)in dry THF (10.0 mL) and the resulting reaction mixture was stirred at70° C. for 3 h. The completeness of the reaction was confirmed by TLCanalysis. The volatiles were evaporated under reduced pressure to yieldcrude compound. The crude compound was purified by silica gel columnchromatography (Eluent: 0-33% ethyl acetate in hexane) and resulted in0.55 g of compound 14e. LCMS: 907.4 (M+H)⁺.

Step 14d:

To a solution of compound 14e (0.55 g, 0.55 mmol) in trifluoroaceticacid (9.5 mL), triisopropylsilane (0.25 mL) and water (0.25 mL) wereadded and stirred at room temperature for 2 h. The resulting solutionwas evaporated under nitrogen to obtain 0.3 g of crude compound 97. Thecrude solid material was purified using preparative-HPLC methoddescribed under experimental conditions. LCMS: 397.0 (M+H)⁺; HPLC:t_(R)=10.547 min.

The below compounds were prepared by procedure similar to the onedescribed in Example 14 (compound 97) with appropriate variations inreactants or amino acids, solvents, quantities of reagents and reactionconditions. The analytical data of the compounds are summarized hereinbelow table.

Compound LCMS HPLC No. Structure (M + H)⁺ (t_(R), min) 98

403.1 14.7 99

439.1 16.9 100

452.4 8.9 101

452.0 — 102

493.4 — 103

438.7 — 104

395.2 10.2

Although the present application has been illustrated by certain of thepreceding examples, it is not to be construed as being limited thereby;but rather, the present application encompasses the generic area ashereinbefore disclosed. Various modifications and embodiments can bemade without departing from the spirit and scope thereof. For example,the following compounds which can be prepared by following similarprocedure as described above with suitable modification known to the oneordinary skilled in the art are also included in the scope of thepresent application:

Example 15: Rescue of Mouse Splenocyte Proliferation in the Presence ofrecombinant PD-L1

Recombinant mouse PD-L1 (rm-PDL-1, cat no: 1019-B7-100; R&D Systems)were used as the source of PD-L1.

Requirement:

Mouse splenocytes harvested from 6-8 weeks old C57 BL6 mice; RPMI 1640(GIBCO, Cat #11875); DMEM with high glucose (GIBCO, Cat #D6429); FetalBovine Serum [Hyclone, Cat #SH30071.03]; Penicillin (10000unit/mL)-Streptomycin (10,000 μg/mL) Liquid (GIBCO, Cat #15140-122); MEMSodium Pyruvate solution 100 mM (100x), Liquid (GIBCO, Cat #11360);Nonessential amino acid (GIBCO, Cat #11140); L-Glutamine (GIBCO, Cat#25030); Anti-CD3 antibody (eBiosciences—16-0032); Anti-CD28 antibody(eBiosciences—16-0281); ACK lysis buffer (1 mL) (GIBCO, Cat #-A10492);Histopaque (density-1.083 gm/mL) (SIGMA 10831); Trypan blue solution(SIGMA-T8154); 2 mL Norm Ject Luer Lock syringe—(Sigma 2014-12); 40 μmnylon cell strainer (BD FALCON 35230); Hemacytometer (Bright line-SIGMAZ359629); FACS Buffer (PBS/0.1% BSA): Phosphate Buffered Saline (PBS) pH7.2 (HiMedia TS1006) with 0.1% Bovine Serum Albumin (BSA) (SIGMA A7050)and sodium azide (SIGMA 08591); 5 mM stock solution of CFSE: CFSE stocksolution was prepared by diluting lyophilized CFSE with 180 μL ofDimethyl sulfoxide (DMSO C₂H₆SO, SIGMA-D-5879) and aliquoted in to tubesfor further use. Working concentrations were titrated from 10 μM to 1μM. (eBioscience-650850-85); 0.05% Trypsin and 0.02% EDTA (SIGMA59417C); 96-well format ELISA plates (Corning CLS3390); BD FACS caliber(E6016); Recombinant mouse B7-H1/PDL1 Fc Chimera, (rm-PD-L1 cat no:1019-B7-100).

Protocol Splenocyte Preparation and Culturing:

Splenocytes harvested in a 50 mL falcon tube by mashing mouse spleen ina 40 μm cell strainer were further treated with 1 mL ACK lysis bufferfor 5 min at room temperature. After washing with 9 mL of RPMI completemedia, cells were re-suspended in 3 mL of 1×PBS in a 15 mL tube. 3 mL ofHistopaque was added carefully to the bottom of the tube withoutdisturbing overlaying splenocyte suspension. After centrifuging at 800×gfor 20 min at room temperature, the opaque layer of splenocytes wascollected carefully without disturbing/mixing the layers. Splenocyteswere washed twice with cold 1×PBS followed by total cell counting usingTrypan Blue exclusion method and used further for cell based assays.

Splenocytes were cultured in RPMI complete media (RPMI+10% fetal bovineserum+1 mM sodium pyruvate+10,000 units/mL penicillin and 10,000 μg/mLstreptomycin) and maintained in a CO₂ incubator with 5% CO₂ at 37° C.

CFSE Proliferation Assay:

CFSE is a dye that passively diffuses into cells and binds tointracellular proteins. 1×10⁶ cells/mL of harvested splenocytes weretreated with 5 μM of CFSE in pre-warmed 1×PBS/0.1% BSA solution for 10min at 37° C. Excess CFSE was quenched using 5 volumes of ice-coldculture media to the cells and incubated on ice for 5 min. CFSE labelledsplenocytes were further given three washes with ice cold complete RPMImedia. CFSE labelled 1×10⁵ splenocytes added to wells containing eitherMDA-MB231 cells (1×10⁵ cells cultured in high glucose DMEM medium) orrecombinant human PDL-1 (100 ng/mL) and test compounds. Splenocytes werestimulated with anti-mouse CD3 and anti-mouse CD28 antibody (1 μg/mLeach) and the culture was further incubated for 72 h at 37° C. with 5%CO₂. Cells were harvested and washed thrice with ice cold FACS bufferand % proliferation was analysed by flow cytometry with 488 nmexcitation and 521 nm emission filters.

Data Compilation, Processing and Inference:

Percent splenocyte proliferation was analysed using cell quest FACSprogram and percent rescue of splenocyte proliferation by compound wasestimated after deduction of % background proliferation value andnormalising to % stimulated splenocyte proliferation (positive control)as 100%. The results are given in Table I.

Stimulated splenocytes: Splenocytes+anti-CD3/CD28 stimulationBackground proliferation: Splenocytes+anti-CD3/CD28+PD-L1Compound proliferation: Splenocytes+anti-CD3/CD28+PD-L1+CompoundCompound effect is examined by adding required conc. of compound toanti-CD3/CD28 stimulated splenocytes in presence of ligand (PDL-1).

TABLE I Percent rescue of splenocyte proliferation data of compounds ofinvention Percent rescue of Compound splenocyte proliferation No. (@100nM) 1 76 2 68 3 73 4 44 5 38 6 69 7 91 8 48 9 84 10 84 11 66 13 62 14 9215 28 16 50 17 58 18 57 19 54 20 51 21 51 23 49 24 17 27 37 28 36 30 6531 42 32 70 33 60 34 59 35 66 36 68 37 60 38 52 39 75 40 67 41 78 42 5043 60 44 71 45 17 46 53 47 49 51 20 52 71 56 26 60 99 62 35 75 119 76 6777 75 78 42 79 37 80 55 81 18 82 12 83 34 84 71 88 10 89 54 90 66 94 9795 30 101 70 102 38 103 79

We claim:
 1. A compound of formula (I):

or a pharmaceutically acceptable salt thereof; wherein, X is O or S; R₁and R₂ are each independently a side chain of an amino acid, hydrogen,(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl or cycloalkyl; wherein each(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl or cycloalkyl is optionallysubstituted by one or more substituents, selected from amino,alkylamino, acylamino, carboxylic acid, carboxylate, carboxylic acidester, thiocarboxylate, thioacid, —CONR₇R₈, hydroxy, cycloalkyl,(cycloalkyl)alkyl, aryl, arylalkyl, heterocyclyl, (heterocyclyl)alkyl,heteroaryl, (heteroaryl)alkyl, guanidino, —SH and —S(alkyl); optionallywherein cycloalkyl, aryl, heterocyclyl or heteroaryl is furthersubstituted by one or more substituents and optionally wherein two orthree carbon atoms of the (C₁-C₆)alkyl, (C₂-C₆)alkenyl or (C₂-C₆)alkynylform part of a 3-7-membered carbocyclic or heterocyclic ring; R₃ is—S(O)_(p)-[Aaa1]_(m); R₆ is hydrogen, alkyl, aminoalkyl, hydroxyalkyl,alkoxyalkyl, or acyl; R₇ and R₈ independently are hydrogen,(C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, aryl or heterocyclyl;wherein each (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, aryl orheterocyclyl is optionally substituted by one or more substituentsselected from halogen, hydroxyl, amino, nitro, cyano, cycloalkyl,heterocyclyl, heteroaryl, aryl, guanidino, (cycloalkyl)alkyl,(heterocyclyl)alkyl and (heteroaryl)alkyl; optionally wherein two orthree carbon atoms of the (C₁-C₆)alkyl, (C₂-C₆)alkenyl or (C₂-C₆)alkynylform part of a 3-7-membered carbocyclic or heterocyclic ring; oralternatively R₇ and R₈ together with the nitrogen to which they areattached form an optionally substituted 3-7-membered ring containing 0-2additional heteroatoms independently selected from N, O and S in anystable combination; wherein the optional substituent at each occurrenceis selected from hydroxyl, —COOH, —COO-alkyl, amide, halo, amino, nitroand cyano; [Aaa1] represent an amino acid residue having a side chain;wherein a C-terminal carboxyl moiety of the amino acid residue is a freeC-terminal carboxyl moiety or an alkyl substituted C-terminal carboxylmoiety or the C-terminal moiety is optionally substituted amido, oroptionally substituted heteroaryl, and an N-terminal amino moiety of theamino acid residue is a free N-terminus; R_(a) is hydrogen or alkyl;R_(b) is hydrogen, alkyl, aminoalkyl, hydroxyalkyl or alkoxyalkyl; orR_(b) and R₂, together with the atoms to which they are attached, formpyrrolidine or piperidine, each optionally substituted with one or moresubstituents independently selected from hydroxyl, halo, amino, cyanoand alkyl; m is 1, 2, or 3; and p is 1 or
 2. 2. The compound of claim 1,wherein the compound is of formula (IA):

or a pharmaceutically acceptable salt thereof.
 3. The compound of claim1, wherein R_(b) is H.
 4. The compound of claim 1, wherein the sidechain of [Aaa1] comprises a (C₁-C₄)alkyl optionally substituted by oneor more substituents, selected from amino, alkylamino, acylamino,carboxylic acid, carboxylate, thiocarboxylate, thioacid, —CONR₇R₈,hydroxy, cycloalkyl, (cycloalkyl)alkyl, aryl, heterocyclyl, heteroaryl,guanidino, —SH, and —S(alkyl); optionally wherein cycloalkyl, aryl,heterocyclyl or heteroaryl.
 5. The compound of claim 1, wherein the sidechain of [Aaa1] comprises a (C₁-C₄)alkyl substituted by one or moresubstituents, selected from amino, acylamino, carboxylic acid, —CONR₇R₈,hydroxy, cycloalkyl, aryl, heteroaryl, guanidino, —SH and —S(alkyl); andwherein R₇ and R₈ independently are hydrogen, alkyl, aryl orheterocyclyl.
 6. The compound of claim 1, wherein R_(a) is H.
 7. Thecompound of claim 1, wherein R₁ is (C₁-C₈)alkyl optionally substitutedby one or more substituents, selected from amino, alkylamino, acylamino,carboxylic acid, carboxylate, carboxylic acid ester, thiocarboxylate,thioacid, —CONR₇R₈, hydroxy, cycloalkyl, (cycloalkyl)alkyl, aryl,arylalkyl, heterocyclyl, (heterocyclyl)alkyl, heteroaryl,(heteroaryl)alkyl, guanidino, —SH, and —S(alkyl); and optionally whereincycloalkyl, aryl, heterocyclyl or heteroaryl.
 8. The compound of claim1, wherein R₁ is (C₁-C₈)alkyl substituted by one or more substituentsselected from amino, acylamino, carboxylic acid, —CONR₇R₈, hydroxy,cycloalkyl, aryl, heteroaryl, guanidino, —SH, and —S(alkyl); and whereinR₇ and R₈ independently are hydrogen, alkyl or aryl.
 9. The compound ofclaim 1, wherein R₁ is the side chain of an amino acid.
 10. The compoundof claim 1, wherein R₁ is a side chain of an amino acid selected fromAla, Asn, Asp, Tyr, Lys, Ser, Thr, Gln, Ile, Val, Glu, Arg, Leu, Trp,His, Met, Cys, and Phe.
 11. The compound of claim 1, wherein R₂ is(C₁-C₈)alkyl optionally substituted by one or more substituents,selected from amino, alkylamino, acylamino, carboxylic acid,carboxylate, carboxylic acid ester, thiocarboxylate, thioacid, —CONR₇R₈,hydroxy, cycloalkyl, (cycloalkyl)alkyl, aryl, arylalkyl, heterocyclyl,(heterocyclyl)alkyl, heteroaryl, (heteroaryl)alkyl, guanidino, —SH, and—S(alkyl); and optionally wherein cycloalkyl, aryl, heterocyclyl orheteroaryl.
 12. The compound of claim 1, wherein R₂ is (C₁-C₈)alkylsubstituted by one or more substituents, selected from amino, acylamino,carboxylic acid, —CONR₇R₈, hydroxy, cycloalkyl, aryl, heteroaryl,guanidino, —SH and —S(alkyl); and wherein R₇ and R₈ independently arehydrogen or alkyl.
 13. The compound of claim 1, wherein R₂ is the sidechain of an amino acid.
 14. The compound of claim 1, wherein R₂ is aside chain of an amino acid selected from Ala, Asn, Ile, Lys, Phe, Glu,Asp, Trp, Val, Ser, Gln, Tyr, Thr, Met, Arg, and Leu.
 15. The compoundof claim 1, wherein R_(b) and R₂, together with the atoms to which theyare attached, form pyrrolidine or piperidine, optionally substitutedwith one or more substituents, independently selected from hydroxyl,halo, amino, cyano and alkyl.
 16. The compound of claim 1, wherein R₆ isH.
 17. The compound of claim 1, wherein at least one of the amino acidresidues is a D amino acid residue.
 18. The compound of claim 1, whereinat least one of the amino acid residues is an L amino acid residue. 19.The compound of claim 1, wherein the compound is: Compound No. Structure97

98

99

100

101

102

103

104

119

120

121

122

123

124

or a pharmaceutically acceptable salt thereof or a stereoisomer thereof.20. A pharmaceutical composition comprising a compound of claim 1 and apharmaceutically acceptable carrier.